Internet Routing and BGP Looking Glasses

Summary

From time to time I get requests from colleagues, “Can you ping this address?”. Many times what is going on is they are bringing up a new internet link and want to check routing. Sometimes they areadding a public endpoint and want to make sure its accessible. They are asking me because within their network it works but they need to make sure it is accessible or routing properly over the internet.

BGP Looking Glasses are a great tool for this if you would like to be self sufficient. You can also get a wider view than just a few colleagues. My favorite one is HE.net’s https://lg.he.net

What is BGP?

BGP Stands for Border Gateway Protocol. It is the standard exterior gateway protocol for internet routing. While an internal network may use something like OSPF for its interior, BGP is better suited for exterior routing.

One of the few keys to understanding BGP at a high level is to understand it is a distance vector routing protocol. These routes are typically better suited for WAN routing as they are a bit more light weight. The downside is that each router’s perception of the internet is key. There is no unified single view of the internet routing. Each router has its own perception of the internet based on the BGP routes it receives.

This is why Looking Glasses are so important. You can see the perception of various points on the internet. This can help you determine internet traffic destined to your infrastructure is taking the expected and optimal path.

HE.net’s Looking Glass

Here is a small snippit of HE’s LG. They have various routers all over the world that would not fit into this screen shot. You can also see the various functions you can perform on the right hand side.

HE.net Looking Glass
HE.net Looking Glass

Ping and traceroute are fairly self explanatory. For ping it just returns the results of an ICMP ping and traceroute shows a list of routers in the path of getting to the destination.

HE.net Looking Glass - Traceroute
HE.net Looking Glass – Traceroute

The real value here is the “BGP Route” option.

HE.net BGP Looking Glass Details
HE.net Looking Glass BGP Details

Here we can see all of the BGP peers this particular router has learned the route to 1.1.1.0/24, the AS path it takes and which one it selects as the best path.

Autonomous Systems

If you are new to BGP and dynamic routing protocols you may be wondering what an AS (Autonomous System) is. In BGP world, it is basically a grouping of similar routers that announce a similar set of subnets or prefixes as they are called in BGP. BGP groups systems together by AS. As each router learns a route, it appends its own AS to the AS path before passing it along.

The above is a bad example because it shows a single direct AS path as HE appears to be directly peered with CloudFlare (AS 13335). CloudFlare is very well peered on the internet. Below is a better example. It at least shows it passing through AS 1299 (Telia) to AS 174 (Cogent)

It seems HE.net is fairly well peered but here is another router output that shows some decent AS paths and the differences. AS 174 being Cogent and AS 209 being CenturyLink and AS 3356 being Level3 it chooses the shortest AS path. Keep in mind the traceroute through CenturyLink could possibly be shorter actual router hops. A shorter AS path does not necessarily mean less latency or shorter traceroute hops.

#show ip bgp 73.0.0.0/8 
BGP routing table entry for 73.0.0.0/8, version 767462940
Paths: (2 available, best #1, table default)
  Advertised to update-groups:
     18        
  Refresh Epoch 1
  174 7922, (received & used)
    X.X.X.X from X.X.X.X (X.X.X.X)
      Origin IGP, metric 13031, localpref 100, valid, external, best
      Community: 174:21000 174:22013
      rx pathid: 0, tx pathid: 0x0
  Refresh Epoch 3
  209 3356 7922, (received & used)
    X.X.X.X from X.X.X.X (X.X.X.X)
      Origin IGP, metric 7800026, localpref 100, valid, internal
      rx pathid: 0, tx pathid: 0

Final Words

If you ever find yourself needing to ping or traceroute from a remote endpoint lg.he.net has you covered. Many carriers have their own looking glass. This is useful incase you want to see how your routes are perceived from their end. If you use BGP at your edge and receive full routes, this is another avenue of seeing those prefixes. With looking glasses, you can do this from various endpoints across the internet pretty easily.

OpenVPN with Encrypted Private Key – Issue Resolved

Summary

I was working on Azure Client VPN with OpenVPN and in testing I had removed the passphrase on the private key for authentication but wanted to put it back on there and it would not work. Some quick searches did not turn up much other than common complaints of this.

Reason

With certificate based authentication on OpenVPN, the public key and private key are put in the ovpn file. This is not the most secure with an unencrypted private key as anyone can simply obtain the file and connect.

With a passphrase on it, there is less concern over the ovpn being disseminated and the key reused.

Issue

The OpenVPN client logs indicated the following

2019-12-20 12:22:42-0600 [-] OVPN 40_89_167_211_p4967 ERR: ">FATAL:CLIENT_EXCEPTION: connect error: PEM_PASSWORD_FAIL: mbed TLS: error parsing config private key : PK - Private key password can't be empty"
2019-12-20 12:22:42-0600 [MyOMIClient,0,] FROM OMI: u">FATAL:CLIENT_EXCEPTION: connect error: PEM_PASSWORD_FAIL: mbed TLS: error parsing config private key : PK - Private key password can't be empty"
2019-12-20 12:22:42-0600 [HTTPChannel,224,] *** API CALL f=xmlrpc_Poll args=['sess_40_89_167_211_p4967_VuxJ7YkTyUVYXeKV_1', 10] kw={} ret=[{'active': True, 'timestamp': 1576866162, 'type': 'ACTIVE', 'last': None}, {'timestamp': 1576866162, 'type': 'FATAL', 'error': u"CLIENT_EXCEPTION: connect error: PEM_PASSWORD_FAIL: mbed TLS: error parsing config private key : PK - Private key password can't be empty"}]

It seemed like it was just not prompting me to enter the passphrase and using a blank one.

Solution

I came across the following article ( https://github.com/pivpn/pivpn/issues/372 ) which had quite a few tangents on it but most recently someone indicated using OpenVPN Connect 3.1.0 and it worked. I tried that and was surprised, it actually prompts me for the passphrase!

It seems the community version of the OpenVPN GUI client supported this but the OpenVPN Connect lacked the feature until recently. As of the time of this writing 3.1.0 is Beta but seems to work great!

I had tried upgrading from 2.5 to 2.7 without luck. Finally after installing 3.1.0 it worked again.

Azure Client VPN with OpenVPN

Summary

In my article Intro To Azure Active Directory Domain Services we discussed environments with minimal infrastructure. With all of the RDP exploits it is typically best not to expose RDP over the internet. Since Bastion is not yet fully available the next best thing aside from setting up a VPN appliance is to use the Point-to-site functionality of a Virtual Network Gateway.

Prerequisites

The first pre-requisite for client VPN using a Virtual Network Gateway is to actually provision one. For OpenVPN compatibility it does require at least SKU VpnGw1 and will not work with basic.

It will require 2 subnets, one for the inside leg of the gateway and another for the client-side pool.

The Virtual Network Gateway does want an inside subnet dedicated for use to the Virtual Network Gateway and not shared amongst other devices.

Authentication is handled either via radius or certificate based. If you are reading this article for a minimized infrastructure you probably do not have radius servers.

Provisioning

The provisioning process is fairly simple although it can take 30-60 minutes for the Virtual Network Gateway to fully provision before you can use the Point-to-site configuration. There are a few simple questions.

Virtual Network Gateway - Create
Virtual Network Gateway – Create

That’s really it for the initial provisioning.

Configuration

Some basic Point-to-site configurations need to be set.

Point-to-site configuration
Point-to-site configuration

The next part is the most difficult part of this. A root and at least one child certificate have to be provisioned. Microsoft has some good documentation on it. To do in Powershell, it does require Windows 10 or Server 2016 or higher.

Root Certificate
Root Certificate

The name is arbritrary but the “Public certificate data” is the area between the “—BEGIN CERTIFICATE—” section and the “—END CERTIFICATE”

The following Microsoft article describes and outlines the process much better than I can do so I will just share it here – https://docs.microsoft.com/en-us/azure/vpn-gateway/vpn-gateway-certificates-point-to-site

Client Configuration

Again – Microsoft does a really good job on instructions for configuring the client so I will just share this link – https://docs.microsoft.com/en-us/azure/vpn-gateway/vpn-gateway-howto-openvpn-clients

Final Words

It can be a pain for those of us not familiar with certificates and command line tools like openssl. The idea is that you have a root certificate authority that then issues individual certificates per user or group of users. If that key becomes compromised you can then revoke the individual certificate or untrust the entire certificate authority. I like the idea of creating a CA chain per organization you grant access to.

In this article we walked through creating the resources required and configuring. We did rely heavily upon the Microsoft documentation but it was fairly complete and well shown.

Make sure you distribute your ovpn files with encrypted private keys! – OpenVPN with Encrypted Private Key – Issue Resolved

Intro To Azure Active Directory Domain Services

Summary

Recently I got the pleasure to stand up Azure Active Directory Domain Services (AADDS) for a client. It has some specific use cases and limitations but can be great for your environment.

This article walks you through the background, some of the limitations and also how to provision.

What is Azure Active Directory Domain Services?

This is a natural question. At a high level, let’s talk about the use case for it. In a small cloud environment with a minimal number of VMs, standing up redundant Domain Controllers can chew up a bit of your budget. From there you have to manage and monitor the domain controllers.

AADDS is a managed platform for this. On the back end it appears to be appliances that provide most of the functionality of Active Directory but with some limitations. It also offers a one way sync from Azure Active Directory (AAD) to AADDS. This allows you to use Azure Active Directory credentials to login to VMs.

Use Case

As touched on above, most administrators want a central credential repository for their cloud VMs. If they are used to Active Directory on prem but want to tie this to Azure AD, AADDS makes sense, particularly in small environments where there may not be a full budget to host, manage and maintain full domain controllers with adequate redundancy.

Limitations

There are some notable limitations so if you are looking for the full flexibility of native Domain Controllers, AADDS is not that.

One Way Replication

Replication only occurrs from AAD to AADDS. You can make changes in AADDS via normal Active Directory Users and Computers (ADUC) or other tools but they do not replicate back to AAD. AAD can however overwrite these changes.

Azure Active Directory does support AD Connect to connect to on prem domain controllers but it is not compatible with AADDS at this time.

No Custom Attributes

It does not support extending the schema or adding extra custom attributes

External Guests

While external guest accounts will replicate into AADDS, their password and hashes are inaccessible so you will not be able to login under these accounts. An AAD account local to tenant AD will have to be provisioned.

Lack of Control

When you create or change AAD attributes, you have no control over the replication interval. The initial sync may take an hour or two. The provisioning of AADDS takes quite a bit of time as well. In practice, on a smaller environment, replication does seem to happen within 5-15 minutes.

Provisioning

The first step is to select this from the Market and click create

Azure AD Domain Services
Azure AD Domain Services

On the basics tab, pay particular attention to the DNS Domain name. Best practices for domain naming has changed over the years. These settings cannot be changed after implementing.

Azure AD Domain Services - Basics
Azure AD Domain Services – Basics

For reference here is the output of the “Help me choose the DNS name”. Also – here is another Microsoft article on best practices – https://social.technet.microsoft.com/wiki/contents/articles/34981.active-directory-best-practices-for-internal-domain-and-network-names.aspx

Picking Active Directory DNS Name
Picking Active Directory DNS Name

On the networking tab it will by default create a new Virtual Network and Subnet. You can choose an existing virtual network which is highly likely. It does however, indicate you should use a not in use subnet for this. I have not found much information on that but it may have to do with the Network Security Group it creates and applies.

Azure AD Domain Services - Networking
Azure AD Domain Services – Networking

On the next screen you will elect who can manage this environment. Users in this group will function as the “Domain Admins” you are used to in Active Directory.

Azure AD Domain Services - Administration
Azure AD Domain Services – Administration

Next we can choose which objects to synchronize but typically it will be all objects. If you think you may want to scope it though, choose that first as you can go from scoped to all but have to recreate to reverse.

Azure AD Domain Services - Synchronization
Azure AD Domain Services – Synchronization

Finally, we review the config but pay note to this. In order for this all to work, your AAD hashes have to be stored in the AADDS.

Azure AD Domain Services - Review & Create
Azure AD Domain Services – Review & Create

Final Words

In this article we gave a brief overview of Azure Active Directory Domain Services and some use cases. We also went over some limitations and cases where it would not be a good fit. Finally we walked through the actual deployment.

Parsing CSV Files with Golang

Summary

I love coming across problems that require me to learn something new. I have written a few posts about Go (or Golang) such as Using Recursion on Golang to Solve a Problem and Unit Testing Golang on App Engine. Go is one of my favorite utility languages.

Earlier this year, my wife decided to start her own hair salon and do booth rental (Pretty Hare Salon). We set up square for appointment setting and credit cards. It has nice reporting features but there is literally no forecasting. Forecasting helps us determine pricing and when to increase or decrease marketing/advertisement.

Parameters of the Problem

To work around this lack of forecasting, I found an export feature that exports appointments in csv. Unfortunately it does not list the pricing associated with it. At the time, I implemented something in perl but decided to rewrite in Golang. The application inputs two CSV files (1 – appointments and 2 – pricing) and calculates weekly totals based on that.

Helper Function

Error checking and reporting requirements are fairly minimal for this so I use a helper function that is fairly basic.

func CheckErr(err error) {
	if err != nil {
		log.Fatal(err)
	}
}

Loading CSVs

In order to load the CSV into a variable, I opted to use os.Open() which takes the file path. I pass these in through command-line arguments using os.Args. os.Open returns a pointer to a file.

args := os.Args

	appointmentsFile := args[1]
	pricesFiles := args[2]

	af, err := os.Open(appointmentsFile)
	CheckErr(err)

	pf, err := os.Open(pricesFiles)
	CheckErr(err)

I then open the files return by these with cvs.NewReader

appointments := csv.NewReader(af)
prices := csv.NewReader(pf)

NewReader() expects an io.Reader but *os.File implements a reader so we are good.

These readers return a 2 dimensional slice with the left most dimension being the line number and second dimension being the field.

For the price records I read it in entirety. It is not very long.

priceRecords, err = prices.ReadAll()
CheckErr(err)

Iterating the CSV Line by Line

The Appointment file is the full history and we do not need all the data in it. It can get very large over time so it is best not to completely load it into memory. We also will have logic to ignore anything older than 2 weeks as this is a forecast and we do not care about historicals.

for {
	appointment, err := appointments.Read()
	if err == io.EOF {
		break
	}
	// Business logic in here
}

The appointment array in this can then be read as a single dimension. Something similar to what is below exists in the for loop previously shown.

if appointment[2] == "accepted" {
	// More business logic here
}

Looking Up Data

The pricing information which we fully loaded into the two dimensional slice can be iterated as follows

for _, price := range priceRecords {
	if price[0] == service {
		return strconv.ParseFloat(price[8][1:], 64)
	}
}

return 0, errors.New("Could not find service - " + service)

The “service” variable is the service we are looking up. In the price slice, the first or 0 position is the actual service name we are looking up and position 8 is the actual price.

The price field (8) has a dollar sign so I just used string slicing to omit the first character which is the dollar sign so I could parse the float like this

price[8][1:]

The pricing file is highly controlled so I have very little error checking here.

Final Words

In this article we discussed opening and iterating through CSV files using two methods. One involves fully loading the file into memory and the other involves iterating line by line. At this point you should have a good idea of which method to use and when.

Using Recursion on Golang To Solve A Problem!

Summary

I was writing an SSL Certificate Decoder ( https://tools.woohoosvcs.com/certdecoder/ ) and came across an interesting problem. I wanted to validate a certificate chain but had some difficulty figuring it out. The problem was that I needed to find the most child certificate in a seemingly random list of certificates. What I am calling the most child certificate is the one at the bottom of the chain that is issued but does not issue one of its own. Users can provide the cert chain in any order so we cannot relay on the order they are submitted for this tool.

SSL Certificate Chains

To understand the problem, one needs to understand an SSL Certificate Chain. When traversing a chain, each certificate is an individual certificate. How they are linked is by their issuer. There is a subject section about the certificate itself and then an issuer section which indicates the certificate authority certificate that issued that. It goes all the way up until you hit a root certificate. The root certificates sign themselves.

Here you can see the cert chain for this site. The SAN or alternate names that allow tools.woohoosvcs.com be valid are further down below this screenshot.

SSL Certificate Chain
SSL Certificate Chain

Recursion

It had been a few decades since I sat in a Computer Science class but I do remember a few control structures. One of which was recursion. Recursion can be a difficult concept to grasp and an even more difficult concept to implement. Golang has an example of this here. At a high level a recursive function is one that calls itself. The call stack gets nested in each layer. In the case that you do not know how many certificates and iterations you need to go through to find the chain, recursive functions help with this. Alternatively you would have to use multiple layers of “for” loops to iterate through, matching the current cert against one that may be a child. In a past life I may have implemented a few layers of “for” loops to statically account for the most common scenarios.

Recursion can be tricky and if you do not use it right, it can involve stack overflows if the function indefinitely calls it self. The key to a good recursive function is a way out. It needs to be able to exit without continuing to call itself forever. There are also limits based on the platform as to how deep you can go in this recursion. Your platform will have a limit at which point an exception or error is thrown.

For a much better description of recursion you can read the Wikipedia article here – https://en.wikipedia.org/wiki/Recursion_(computer_science)

The Code

It is still a work in progress but after iterations of playing with linked lists, multiple for loops, this is what I landed on.

func findChildOfCert(certs []x509.Certificate, cert x509.Certificate) x509.Certificate {
	if len(certs) <= 1 {
		return cert
	}
	result := cert
	for _, item := range certs {
		if item.Issuer.CommonName == cert.Subject.CommonName {
			return findChildOfCert(certs, item)
		}
	}

	return result
}

It is kicked off in a parent function via

childCert := findChildOfCert(cs, cs[0])

Where cs is a slice (Golang speak for array) of certificates much like “certs” in the recursive function. We pass it the list of certificates and the very first one.

On the first call it checks to see if this certificate issued any others in the list. If so, it calls the function again with the issued certificate( more child than the current ) and does the process over again.

When it cannot find a certificate issued by the currently iterated certificate (most child record), the for loop exits and it simply passes the original cert that the function was called with. At that point, the stack completely unwinds, passing the “answer” certificate all the way down. That result is provided to the childCert variable.

Validating the Cert

Golang provides a few options for validating the cert. Once you have the most child certificate, you can do something like the below.

for i := range cs {
	if !cs[i].Equal(&childCert) {
		roots.AddCert(&cs[i])
	}
}

opts := x509.VerifyOptions{
	Intermediates: roots,
}

opts2 := x509.VerifyOptions{
	Roots: roots,
}

if _, err := childCert.Verify(opts); err != nil {
	status = append(status, "Not Trusted By Root - failed to verify certificate: "+err.Error())
} else {
	status = append(status, "Trusted Chain")
}

if _, err := childCert.Verify(opts2); err != nil {
	status = append(status, "Not Valid(contiguous) - failed to verify certificate: "+err.Error())
} else {
	status = append(status, "Valid Chain")
}

I load up a “roots” slice of the roots provided. I also exclude the child certificate from this. From there I perform two validations. One that the chain is trusted, meaning it rolls up to one that is trusted by the source used. The other validation is that the chain is valid. Is there continuity in the chain or is it broken. A chain can be valid but un trusted. Knowing the difference may help you in a rare case.

Stack Overflow

I actually found a stack overflow doing a regression test with a self signed certificate. The code above actually ended up comparing the certificate to itself over and over again and trying to keep going down the rabit hole. It ended up with the following

runtime: goroutine stack exceeds 1000000000-byte limit
fatal error: stack overflow

runtime stack:
runtime.throw(0x1332651, 0xe)
	/usr/local/go/src/runtime/panic.go:774 +0x72
runtime.newstack()
	/usr/local/go/src/runtime/stack.go:1046 +0x6e9
runtime.morestack()
	/usr/local/go/src/runtime/asm_amd64.s:449 +0x8f

goroutine 24 [running]:
tools.woohoosvcs.com/certdecoder.findChildOfCert(0xc0000d6b00, 0x1, 0x1, 0xc0000b8800, 0x3da, 0x3ea, 0xc0000b8804, 0x2c2, 0x3e6, 0xc0000b89a0, ...)

tools.woohoosvcs.com/certdecoder/certdecoder.go:180 +0x1d0 fp=0xc020114ef8 sp=0xc020114ef0 pc=0x128a210
tools.woohoosvcs.com/certdecoder.findChildOfCert(0xc0000d6b00, 0x1, 0x1, 0xc0000b8800, 0x3da, 0x3ea, 0xc0000b8804, 0x2c2, 0x3e6, 0xc0000b89a0, ...)

tools.woohoosvcs.com/certdecoder/certdecoder.go:184 +0x1a3 fp=0xc020116920 sp=0xc020114ef8 pc=0x128a1e3
tools.woohoosvcs.com/certdecoder.findChildOfCert(0xc0000d6b00, 0x1, 0x1, 0xc0000b8800, 0x3da, 0x3ea, 0xc0000b8804, 0x2c2, 0x3e6, 0xc0000b89a0, ...)

tools.woohoosvcs.com/certdecoder/certdecoder.go:184 +0x1a3 fp=0xc020118348 sp=0xc020116920 pc=0x128a1e3

Luckily my unit testing caught this and this would have never gone to production due to that unit testing. If you’re not sure what unit testing is check out my article Unit Testing Golang on App Engine. The fix was simple though in that to make sure my recursive function doesn’t compare a cert to itself using the .IsEquals() function

Final Words

In this we walked through a useful use case for recursion and the background of the technology that needed it. I even provided some of the errors that happen when you fail to use recursion properly as I accidentally did!

Unit Testing Golang on App Engine

Summary

If you have landed here, it is most likely because you attempted to implement the subject and ran into errors. In my use case, I ran into errors when splitting up my Golang app into packages and added unit testing to it. To compound it, I was automatically deploying via triggers with CloudBuild.

This builds upon the article IP Subnet Calculator on Google App Engine. Reading that article will help give you a good reference point for this article.

This article is not a “How To” on actual unit testing but getting it to work under this unique combination of tools. A great unit testing article I found is here – https://blog.alexellis.io/golang-writing-unit-tests/

How To Setup

Before we talk about what might have gone wrong, let’s talk about how to set this up properly. There has been a lot of confusion since Golang went to version 1.11 and started supporting modules. After supporting modules it appears using GOPATH is a less of a supported method. With that said some tools still look for it.

Directory Structure

To get a final state visual of my directory structure, it ended up as follows

tools.woohoosvcs.com
tools.woohoosvcs.com/app.yaml
tools.woohoosvcs.com/go.mod
tools.woohoosvcs.com/subnetcalculator
tools.woohoosvcs.com/subnetcalculator/subnetcalculator.go
tools.woohoosvcs.com/subnetcalculator/subnetcalculator_test.go
tools.woohoosvcs.com/cloudbuild.yaml
tools.woohoosvcs.com/html
tools.woohoosvcs.com/html/root.html
tools.woohoosvcs.com/html/view.html
tools.woohoosvcs.com/README.md
tools.woohoosvcs.com/static
tools.woohoosvcs.com/static/submitdata.js
tools.woohoosvcs.com/static/subnetcalculator.css
tools.woohoosvcs.com/root
tools.woohoosvcs.com/root/root.go
tools.woohoosvcs.com/main.go

Modules

Modules help with the dependency needs of Golang applications. Previously, private packages were difficult to manage as well as specific versioned public packages. Modules helps many of these issues. Here is a good article on modules – https://blog.golang.org/using-go-modules

The key to my issues seemed to be involving modules. Google App Engine’s migrating to 1.11 guide recommends the following.

The preferred method is to manually move all http.HandleFunc() calls from your packages to your main()function in your main package.

Alternatively, import your application’s packages into your main package, ensuring each init() function that contains calls to http.HandleFunc() gets run on startup.

https://cloud.google.com/appengine/docs/standard/go111/go-differences

My app’s directory is “tools.woohoosvcs.com” so I named the root, the same. Run “go mod init”

$ go mod init tools.woohoosvcs.com
go: creating new go.mod: module tools.woohoosvcs.com
[email protected] tools.woohoosvcs.com % cat go.mod
module tools.woohoosvcs.com

go 1.13

Importing Private Packages

This then lets us to refer to packages and modules under it via something similar.

import ( "tools.woohoosvcs.com/subnetcalculator" )

CloudBuild

My cloudbuild.yaml ended up as follows

steps:
  - id: subnetcalculator_test
    name: "gcr.io/cloud-builders/go"
    args: ["test","tools.woohoosvcs.com/subnetcalculator"]
    #We use modules but this docker wants GOPATH set and they are not compatible.
    env: ["GOPATH=/fakepath"]
  - name: "gcr.io/cloud-builders/gcloud"
    args: ["app", "deploy"]

Interesting tidbit is the “name” is a docker image from Google Cloud Repository or gcr.io

The first id runs the “go” image and runs “go test tools.woohoosvcs.com/subnetcalculator”. It seems the go image wants GOPATH but go test fails with it set so I had to set it to something fake.

It then uses the gcloud deployer which consumes app.yaml

How I Got Here

Unit tests drove me to wanting to split out logic, particularly the subnetcalculator (check it out via https://tools.woohoosvcs.com/subnetcalculator )

Before implementing modules I could get it to run locally by importing ./subnetcalculator but then “gcloud app deploy” would fail.

2019/11/22 01:39:13 Failed to build app: Your app is not on your GOPATH, please move it there and try again.
building app with command '[go build -o /tmp/staging/usr/local/bin/start ./...]', env '[PATH=/go/bin:/usr/local/go/bin:/builder/google-cloud-sdk/bin/:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin HOSTNAME=ace17fcba136 HOME=/builder/home BUILDER_OUTPUT=/builder/outputs DEBIAN_FRONTEND=noninteractive GOROOT=/usr/local/go/ GOPATH=/go GOPATH=/tmp/staging/srv/gopath]': err=exit status 1, out=go build: cannot write multiple packages to non-directory /tmp/staging/usr/local/bin/start.

The error was vague but I noticed it was related to the import path. I tried moving the folder to $GOPATH/src and it seemed to deploy via “gcloud app deploy” but then failed via CloudBuild automated trigger.

------------------------------------ STDERR ------------------------------------
2019/11/21 21:31:39 staging for go1.13
2019/11/21 21:31:39 GO111MODULE=auto, but no go.mod found, so building with dependencies from GOPATH
2019/11/21 21:31:39 Staging second-gen Standard app (GOPATH mode): failed analyzing /workspace: cannot find package "tools.woohoosvcs.com/subnetcalculator" in any of:
	($GOROOT not set)
	/builder/home/go/src/tools.woohoosvcs.com/subnetcalculator (from $GOPATH)
GOPATH: /builder/home/go
--------------------------------------------------------------------------------

ERROR
ERROR: build step 0 "gcr.io/cloud-builders/gcloud" failed: exit status 1

It was like a balancing act with a 3 legged chair! Once I initialized the module though and adjusted the imports it worked great

Final Worlds

Here we worked through a best practice of using modules and an internal package to do automated build deploy on Google App Engine. Unit testing with automated deploys are important so that broken builds do not get pushed to production.

IP Subnet Calculator on Google App Engine

Summary

Over the past few days I put a few hours towards writing a web app to perform some basic CIDR subnet calculations. I wanted to both share the link to it ( https://tools.woohoosvcs.com/subnetcalculator/ ). I also wanted to walk through how I deployed it to Google App Engine.

What is a Subnet Calculator?

When provisioning subnets you typically need to determine your requirements. Determining the size of the subnet based on the number of hosts or what the mask will be can take a little bit of time. This is particularly so when you do not calculate this often. Subnet calculators help save some time on this.

Why did I do it?

I have written a few over the years. My early ones were written in C. Golang has a few libraries though in the new package to help with this. I had to use one the other day and figured why not quite my own. While doing this, why not share how to deploy your own app?

Deploying Golang on Google App Engine

In this, we assume you already have the Google SDK. We walked through this in Hello World From Google App Engine Via PHP.

As with any App Engine app, we need an app.yaml. Mine looks like this

runtime: go112

service: tools

handlers:
 - url: /view\.html
   static_files: view.html
   upload: view.html

I have a main.go file and a static view.html file. Since I already have a default service I am calling this one service. That requires I use a dispatch for my custom domain name.

Don’t forget to add the custom domain to the Settings section!

dispatch:
- url: "tools.woohoosvcs.com/*"
  service: tools

The easiest way to get a Golang app running is as follow. The Google App Engine will run the main function in the main package. Google App Engine sets the PORT environment variable.

package main

func main() {
        port := os.Getenv("PORT")
        if port == "" {
                port = "8080"
                log.Printf("Defaulting to port %s", port)
        }

        http.HandleFunc("/subnetcalculator/", viewSubnetCalculator)

        log.Printf("Listening on port %s", port)
        if err := http.ListenAndServe(":"+port, nil); err != nil {
                log.Fatal(err)
        }
}

// This is the main page to view the Subnet Calculator
func viewSubnetCalculator(w http.ResponseWriter, r *http.Request) {
        http.ServeFile(w, r, "./view.html")
}

The best practice for this would dictate a separate main.go importing your own package but if you were familiar enough with that, you may not need this article.

It is out of scope for this article but “http.HandleFunc(“/subnetcalculator/”, viewSubnetCalculator)” tells Golang that the “/subnetcalculator/” URI be directed to the “viewSubnetCalculator” function. That function simply displays the view.html file

From there we simply run the following. I have tools.woohoosvcs.com under the same parent as dispatch.yaml

cd tools.woohoosvcs.com 
gcloud app deploy

cd ..
gcloud app deploy dispatch/dispatch.yaml

Securing Google App Engine

If you use a Web Application Firewall like Cloudflare, don’t forget to ACL GAE to only allow connections from it. Otherwise, it can be completely bypassed

Google App Engine - Firewall
Google App Engine – Firewall

Final Words

This was just a quick and dirty deploy of a golang app to Google App Engine. As with all the apps though, I run them through Cloudflare or at least some sort of Web Application Firewall.

Samsung Galaxy S9 Moisture Detected!

Summary

I was watching cartoons with my 4 year old when I looked down at my phone and all of a sudden saw a water droplet icon. I dragged it town to read a message that indicated moisture was detected in my charging port. This couldn’t be, because I keep my phone nowhere near water. I had no accidents with it that could cause this, even though it is IP68 certified.

What is moisture detection?

S9 - Moisture Droplet
S9 – Moisture Droplet

IFIXIT has a great article on this. When reading up on this, that was the first link I clicked on. If you actually had your phone near water (which is perfectly acceptable on IP68), it has some great steps on rectifying it. In short, the phone has a sensor that can detect water/moisture and will disable the USB port while this detection is active. It helps to avoid a short or damage to the connectors. Apparently it detects this by monitoring resistance between pins.

Other issues like lint or other material could cause similar issues. The key to troubleshooting this is realizing it could be more than just water or moisture.

Other Things To Try

When I ran into this, I ran through the reboot and the hard reset without luck. I blew out with compressed air to no avail. When I did clean out my USB-C port with a toothpick I did find some debris but clearing this did not resolve the issue immediately.

What finally did it for me, which I was slightly surprised it worked was to power off the phone, plug it in and let it fully charge and then power on. I have a feeling the data for the port was cached and it just needed to clear after clearing debris out.

Here are a list of things to try, in this order.

  • Power off phone
  • Try to clean out with tissue and tooth picks
  • Reboot phone
  • Hard reset phone (power button and lower volume)
  • Blow out with compressed air but make sure none of the liquid comes out.
  • Power off and charge to 100% and then power back on
  • Go to Application Settings / USBSettings and clear cache and data and reboot
  • Factory Reset – Option of last resort because nobody likes doing this

Workarounds

If you are absolutely sure you do not have moisture or debris in there but need to charge, here are some options

  • Wireless charge ( this still works )
  • Power off the phone and try to charge powered off (if there is moisture in there this will potentially damage phone)

Sources

Here are a list of URLs I came across in my search. They may also help you further

Final Words

I hope you find this article before you went ahead and factory reset or set in for repair. With that said, even if you cannot get this error to go away, wireless charging still works. You will just be mostly unable to charge via wired. On some phones you can still charge when the phone is powered off.

Virtual Machine Orchestration on GCE

Summary

In this article we tackle VM orchestration. We I touched on in other articles, the desire is to dynamically spin up VMs as necessary. Some of the constructions in Google Cloud that are used are instance templates, instance groups, load balancers, health checks, salt (both state and reactor).

First Things First

In order to dynamically spin up VMs we need an instance group. For an instance group to work dynamically we need an instance template.

Instance Template

For this instance template, I will name it web-test. The name for this is important but we’ll touch on that later on.

GCE - Instance Template - Name
GCE – Instance Template – Name
GCE - Instance Template - CentOS
GCE – Instance Template – CentOS

For this demonstration we used CentOS 8. It can be any OS but our Salt state is tuned for CentOS.

GCE - Automation
GCE – Automation

As we touched on in the Cloud-init on Google Compute Engine article, we need to automate the provisioning and configuration on this. Since Google’s CentOS image does not come with this we use the startup script to load it. Once loaded and booted, cloud-init configures the local machine as a salt-minion and points it to the master.

Startup Script below

#!/bin/bash

if ! type cloud-init > /dev/null 2>&1 ; then
  # Log startup of script
  echo "Ran - `date`" >> /root/startup
  sleep 30
  yum install -y cloud-init

  if [ $? == 0 ]; then
    echo "Ran - yum success - `date`" >> /root/startup
    systemctl enable cloud-init
    # Sometimes GCE metadata URI is inaccessible after the boot so start this up and give it a minute
    systemctl start cloud-init
    sleep 10
  else
    echo "Ran - yum fail - `date`" >> /root/startup
  fi

  # Reboot either way
  reboot
fi

cloud-init.yaml below

#cloud-config

yum_repos:
    salt-py3-latest:
        baseurl: https://repo.saltstack.com/py3/redhat/$releasever/$basearch/latest
        name: SaltStack Latest Release Channel Python 3 for RHEL/Centos $releasever
        enabled: true
        gpgcheck: true
        gpgkey: https://repo.saltstack.com/py3/redhat/$releasever/$basearch/latest/SALTSTACK-GPG-KEY.pub

salt_minion:
    pkg_name: 'salt-minion'
    service_name: 'salt-minion'
    config_dir: '/etc/salt'
    conf:
        master: saltmaster263.us-central1-c.c.woohoo-blog-2414.internal
    grains:
        role:
            - web
GCE – Instance Template – Network tags – allow-health-checks

The network tag itself does not do anything at this point. Later on we will tie this into a firewall ACL to allow the Google health checks to pass.

Now we have an instance template. From our Intro to Salt Stack article we should have a salt server.

SaltStack Server

We have a state file here to provision the state but from our exposure we need salt to automagically do a few things.

Salt is a fairly complex setup so I have provided some of the files at the very bottom. I did borrow many ideas from this page of SaltStack’s documentation – https://docs.saltstack.com/en/latest/topics/tutorials/states_pt4.html

The first thing is to accept new minions as this is usually manual. We then need it to apply a state. Please keep in mind there are security implications of auto accepting. These scripts do not take that into consideration as they are just a baseline to get this working.

In order to have these automatically work, we need to use Salt reactor which listens to events and acts on them. Our reactor file looks like this. We could add some validation, particularly on the accept such as validating the minion name has web in it to push the wordpress state.

{# test server is sending new key -- accept this key #}
{% if 'act' in data and data['act'] == 'pend' %}
minion_add:
  wheel.key.accept:
  - match: {{ data['id'] }}
{% endif %}
{% if data['act'] == 'accept' %}
initial_load:
  local.state.sls:
    - tgt: {{ data['id'] }}
    - arg:
      - wordpress
{% endif %}

This is fairly simple. When a minion authenticates for the first time, acknowledge it and then apply the wordpress state we worked on in our articicle on Salt State. Since we may have multiple and rotating servers that spin up and down we will use Google’s Load Balancer to point Cloudflare to.

Cloudflare does offer load balancing but for the integration we want, its easier to use Google. The load balancer does require an instance group so we need to set that up first.

Instance Groups

Instance groups are one of the constructions you can point a load balancer towards. Google has two types of instance groups. Managed, which it will auto scale based on health checks. There is also managed which you have to manually add VMs to. We will choose managed

GCE - New Managed Instance
GCE – New Managed Instance

This name is not too important so it can be any one you like.

GCE - Instance Group
GCE – Instance Group

Here we set the port name and number, an instance template. For this lab we disabled autoscaling but in the real world this is why you want to set all of this up.

Instance Group - Health Check
Instance Group – Health Check

The HealthCheck expects to receive an HTTP 200 message for all clear. It is much better than a TCP check as it can validate the web server is actually responding with expected content. Since WordPress sends a 301 to redirect, we do have to set the Host HTTP Header here, otherwise the check will fail. Other load balancers only fail on 400-599 but Google does expect only a HTTP 200 per their document – https://cloud.google.com/load-balancing/docs/health-check-concepts

Instance Group Provisioning
Instance Group Provisioning

And here you can see it is provisioning! While it does that, let’s move over to the load balancer.

Firewall Rules

The health checks for the load balancer come from a set range of Google IPs that we need to allow. We can allow these subnets via network tags. Per Google’s Healthcheck document, the HTTP checks come from two ranges.

VPC - Allow Health Checks!
VPC – Allow Health Checks!

Here we only allow the health checks from the Google identified IP ranges to machines that are tagged with “allow-health-checks” to port 443.

Google Load Balancer

Initial

This is a crash course into load balancers if you have never set them up before. It is expected you have some understanding of front end, back end and health checks. In the VPC section we need to allow these

Google Load Balancer - Start configuration
Google Load Balancer – Start configuration
Google Load Balancer - Internet
Google Load Balancer – Internet

Back End Configuration

Google’s load balancers can be used for internal only or external to internal. We want to load balance external connections.

Google Load Balancer - Back End Create
Google Load Balancer – Back End Create

We will need to create a back end endpoint.

Luckily this is simple. We point it at a few objects we already created and set session affinity so that traffic is persistent to a single web server. We do not want it hopping between servers as it may confuse the web services.

Front End Configuration

Health Check Validation

Give the load balancer provisioning a few minutes to spin up. It should then show up healthy if all is well. This never comes up the first time. Not even in a lab!

Google Load Balancer - Healthy!
Google Load Balancer – Healthy!

Troubleshooting

The important part is to walk through the process from beginning to end when something does not work. Here’s a quick run through.

  • On provisioning, is the instance group provisioning the VM?
  • What is the status of cloud-init?
  • Is salt-minion installing on the VM and starting?
  • Does the salt-master see the minion?
  • Reapply the state and check for errors
  • Does the load balancer see health?

Final Words

If it does come up healthy, the last step is to point your DNS at the load balancer public IP and be on your way!

Since Salt is such a complex beast, I have provided most of the framework and configs here – Some of the more sensitive files are truncated but left so that you know they exist. The standard disclaimer applies in that I cannot guarantee the outcome of these files on your system or that they are best practices from a security standpoint.