Coding, How to

How to: Check your DNS entry maps to your Public IP in Bash

I wrote this today as I wanted to ensure that a service waiting for its DNS name to be updated with the correct IP address (its Public IP) before starting.

This little script uses Curl with Akamai’s ‘whatsismyip.akamai.com’ endpoint to get the Public IP and then NSLookup to get the IP returned by the DNS server for the domain. It keeps trying for a while until they match or exits if they don’t match after 250 seconds.

WARNING: In my case it turned out that outbound traffic didn’t route through the same IP as inbound so the script always failed. This may happen to you too if you’re using this in K8s.

WARNING: The AWK logic extracting the IP from the NSLookup is brittle is expects result on line 5. This works on Alpine but may need tweaking, likely are better approaches here.

Run “dnscheck.sh mydns.name.here”

Standard
Apps, Azure, kubernetes

Magic, MutatingAdmissionsControllers and Kubernetes: Mutating pods created in your cluster

I recently wanted to use a Mutating Admissions Controller in Kubernetes to alter pods submitted to the cluster – here is a quick summary of how to do it.

In this case we wanted to change the image pull location, just as a quick example (I’m not sure this is a great idea in a real system as it introduces a single point of failure for pod creation but the sample code should be useful to others).

So how do they work? Well it’s super simple, you register a webhook in K8s which is called when a certain action occurs and you create a receiver which accepts that webhook and responds with a JSONPatch containing any changes you want to make.

Lets try it out, first up you’ll need ngrok, this creates a public endpoint for a port on your machine with an https cert and everything. We’ll use this for testing.

Lets start our webhook receiver locally.

  1. .ngrok http 3000
  2. ​git clone https://github.com/lawrencegripper/MutatingAdmissionsController and CD into the dir
  3. npm install && npm watch-server

Well you register a webhook in kubernetes which is called when certain things happen, in this case we register one to be called when a pod is created:

apiVersion: admissionregistration.k8s.io/v1beta1
kind: MutatingWebhookConfiguration
metadata:
  name: local-repository-controller-webhook
webhooks:
- clientConfig:
    # ngrok public cabundle
    caBundle: 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
    url:  https://1eafed28.ngrok.io/pod
  failurePolicy: Fail
  name: 1eafed28.ngrok.io
  namespaceSelector: {}
  rules:
  - apiGroups:
    - ""
    apiVersions:
    - v1
    operations:
    - CREATE
    resources:
    - pods

 

When our simply Koa.js app, written in Typescript, receives the request it does the following:

  1. Clone the incoming pod spec into a new object
  2. Make changes to the clone, updating the image location
  3. Creates a JSONPatch by comparing the original and the clone
  4. Base64 Encodes the JSONPatch data
  5. Returns the patch as part of an `admissionResponse` object

The code is hopefully nice and simple to follow so take a look at it here. If you’d like a more complex example you can take a look at the golang code here in istio which uses a similar method to inject the istio sidecars  (This is what I read in order to write the Typescript example).

That’s it, nice and simple.

Note: ngrok approach won’t work in an Azure AKS cluster due to networking restrictions, you’ll need an ACE Engine cluster or other.. or you can test inside the cluster with the receive setup as a service but beware of circular references (pod can’t be created because CREATE calls webhook which is received by the pod which can’t be created).

Standard
Azure, Coding

From ARM to Terraform: Why I’m becoming a Terraform convert

Let me give you some background: I’ve been a heavy user of the Azure Resource Manager (ARM) templates for some time now. We’ve had some good times together. We’ve also had some bad times and boy have we seriously fallen out at times!

I’ve used ARM extensively to automate deployment, configuration and update of the infrastructure in Azure. I’ve used it on everything from single-person projects to large scale dual-region deployments of services with critical live traffic.

The takeaway for me has been: ARM is solid, reliable and does what I need – however, it isn’t always the easiest to use and it forces a wall between infrastructure deployment and application configuration which I’ve always found to be painful.

For example, when working with Azure Storage through ARM you can create a storage account, but you can’t create ‘queues’ or upload ‘blobs’ into the account. Another example – you can create an Azure Kubernetes cluster with AKS but you can’t create ‘secrets’ or ‘deployments’ in the cluster.

Shortcomings like these can be painful at times, and difficult to work around.

Typically, an application running in AKS might use a managed Redis Cache instance or an Azure Storage queue. Ideally, you want to use ARM to…

  1. Create your Redis cache
  2. Create your storage queue
  3. Create your AKS cluster
  4. Create secretes in AKS cluster with Redis and Storage access keys
  5. Deploy your container based application.

Once ARM has finished, you want your application set and and ready to go. You don’t want the container to have to check and create queues if they don’t exist. You don’t want it to somehow retrieve the Redis access keys.

But, because you can’t set these things up with ARM you’re unable to deploy a working application in one hit. You have to run ARM to create Redis, AKS and storage then after that you have to run a script which injects the access keys into your AKS cluster so your app can use them. That’s not ideal. (Some interesting integration work between ARM and Terraform is underway which provides an interesting way to merge both but I’m not going into that now. Read more here.)

My other issue with ARM is much more personal and many may disagree, but I find it very hard to author. VSCode has introduced some great ARM tooling which certainly helps make things better, I still find it dense and hard to parse mentally.

ARMvsHCL

ARM (left) vs Terraform (right): VM Creation in Azure

So, what’s the solution?

Recently, I’ve been working with Terraform and I think it helps with a lot of these issues. First up, in my opinion, it’s nice and simple to read. Here is an example creating a storage account and uploading a file into it:

storageAndUpload

Create a storage account with a random name, create a container called ‘scripts’ in it and upload ‘init.sh’ script into the container. Full example here generates a SAS url to the uploaded script.

Terraform is run on your client, which means you can also do more; things that aren’t possible with ARM, such as uploading ‘blobs’ or configuring ‘queues’.

But that’s not really the main thing that has me converted. Terraform is made up of ‘Providers’ which each know how to talk to a set of API’s. Think of these a bit like ‘Resource Providers’ in ARM. Terraform has an Azure provider but it also has a Kuberenetes provider, a CloudFlare provider, a RabbitMQ provider… you get the point.

This is where things really light up. No modern solution of any serious scale is solely confined to one stack/cloud… with Terraform you can reach into all of these by including, or even writing your own, providers. The result is that you have one toolchain and one interface to work with. You can bridge between infrastructure and runtime, taking access keys and injecting them into your k8s cluster as a secret, for example.

You can see an end-to-end example of this with an AKS cluster in my repo here.

“Well that all sounds great Lawrence but what’s the catch?”

Good question. There are, as they’re always are, some downsides to Terraform. Firstly, not all of ARM APIs are provided. There is a nice workaround to this which lets you embed ARM within Terraform which goes a long way to mitigate this issue. You can see an example of that here where I call Azure Batch from Terraform. Some of the docs and examples of Azure are out-of-date or need some tweaking too.  But, it’s an OSS effort so you can (and I have) add functionality for resources that are missing and fix up docs as you go.

Secondly, like any abstraction there are leaks occasionally and where you gain those abstractions it will, ultimately, bite or nip or maybe it won’t, but this depends on what you’re doing and how you’re doing it. For me this hasn’t been a problem…yet.

What else is in this space?

https://pulumi.io/ also just launched which has an interesting take on the deployment/configuration problem but I haven’t yet had a chance to play with it in detail.

Big thanks to @martinpeck for helping with this post!

Standard