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Exploring Immutable Infrastructure with Vault

On by Lorenzo Setale

During the last year, I have been curious about Immutable Infrastructure. After researching, I noticed that I had been applying some of these concepts already to stateless Docker containers, and I wanted to do a practical project with it. So I thought about exploring Immutable Infrastructure and use it to deploy Hashicorp Vault.

Hashicorp Vault Logo

I have shared a git repository with some explanation and examples. It is written with Qm64’s needs in mind and I strongly suggest to go through the comments, and the code before running commands!

A little about Immutable Infrastructure

If you are familiar with stateless workloads on docker/k8s this will be easy! 😜

One of the most prominent concepts that I fell in love with is Pets VS Cattle. Shortly the idea is that instead of maintaining machines alive (as Pets 🐶), and upgrading them constantly, VMs are killed periodically and replaced with new updated versions (like cattle 🐮 we don’t care about them too much).


I believe that Immutable Infrastructure starts from there and expands it a little by forcing VMs to be stateless and limiting, if not forbidding, changes to these machines (ex: No SSH = way fewer changes).

Immutable Infrastructure

Very basically, servers are never modified after they are deployed. If there are errors or changes to be applied, a new VM Image is created, tested and then it will replace the old one1.

The goals

Vault is one of those services that you don’t want to run in an environment that has any other process: you need it to be in its own safe and protected VM. For this reason I believe it is one of the perfect candidates to explore Immutable Infrastructure and to move it out from docker.

My goals for this project are basic and could be extended to almost any service/project. I want to explore Immutable Infrastructure to make sure that:

  • The Virtual Machine has a reduced attack surface
  • The VM doesn’t have more workloads/services (it runs just Vault)
  • I can test the VM before deploying it in production
  • I can rollback quickly to previous versions when needed
  • Humans are not involved for most of the things3 (so no human errors4 )
  • Scaling is easy and automated 2

Using immutable infrastructure also brings other benefits and requires a different mindset compared to “older Operations” methodologies. Still for now I will focus only on these benefits as goals for the project.

The process

The first thing I want to start working on is building the images. To keep this cloud-agnostic I am using Packer and Ansible. Then I will deploy on AWS (as an example) the image using Terraform and Cloud-Init to apply the initial configuration. We will use Cloudflare to manage the DNS records.

Note 1: To ease most of the process I am using make (GNU Make) a lot, the main reason is that I can standardize the commands that I manually run during development with the one that is executed by Gitlab CI/CD pipeline. Please read this to learn more!

Note 2: After the deployment is done, Vault needs to be initialized, this is a one-time process that is done manually and I will ignore it. The repository I am sharing contains also some terraform configuration for Vault’s internal setup used by Qm64. For the post-deploy procedure I strongly suggest to read Vault’s official documentation

Building the image

Building the images is quite easy, but it requires some attention: this is an automated process that forces me to not include any secret or specific configuration. Since this image can be deployed multiple times at the same time, it can’t be tailored with a specific setup/IP/certificate as if it was a pet.

To build the image Packer needs AWS credentials set up. This process can be both automated as well manual (at least at the beginning). I am passing credentials via environmental variables so that Make can use the one in my env or if not present, it will generate the credentials using Vault (if deployed already). Read more about the env variables used by packer here.

As described in the README file I am able to build the image (AMI) by running:

make -c packer validate build \
     -e BUILD_PLATFORM=amazon-ebs

This will call Packer and create a temporary EC2 Instance/VM, it will be used to run some Ansible playbooks in it and install Vault service.

Packer building an instance on AWS

After that, it will stop the AWS EC3 instance, create a snapshot and AMI and then terminate it. Once it is done it will output the AWS AMI (or image name, depending on the platform) that we will use on the next step.

Configuring and Deploying Images/Cattle

This is the core of the concept behind Immutable Infrastructure: Deploying things! Hurray! I am going to make the image/cattle pretty usable! 🤣

example of pretty usable cattle

For this step I have decided to use Terraform. I could have manually implemented it or written a bunch of bash scripts with AWS CLI, but I want to keep this example cloud-agnostic. This step requires a little knowledge related to terraform, please read the official documentation if you are not familiar with it.

Terraform will require the AMI ID we created before. I can provide it via variables (env var too): this could allow me to “chain” Packer with Terraform5 or simply to specify the Image (AMI) to use on the fly.

For example, the following command will show planning to deploy ami-0894b635d1bd24710 image:

make -C infrastructure plan
     -e TF_VAR_vault_ami=ami-0894b635d1bd24710

This will just validate the current setup and show what will happen in AWS and Cloudflare if we apply the changes. Please refer to the source code and the README file to know more about this setup

What about configuration? Well, 😏 I have decided to inject the configuration using Terraform templates and Cloud-init.

In this way, I can instruct Vault to point to the right S3 bucket or to use the right domain, as well as to generate SSL certificates only on deploy time. 🔑 I am using an IAM Profile generated by Terraform to allow the EC2 instance to read the s3 bucket without dealing with keys and permissions or writing secrets into Vault’s configuration files. 😍 I found this step the coolest part!!!

Deploying a new version

If we find out that there is an outdated kernel version or that there is a new Vault version, what we need to do is to rebuild the image. For example:

make -C packer validate build \
     -e BUILD_PLATFORM=amazon-ebs \
     -e VAULT_VERSION=1.3.3

This will create a new image with Vault v1.3.3 and the OS upgraded. Then we can use the image ID in Terraform and use workspaces to test it in a different environment to make sure it works. If we feel safe we can then deploy it:

make -C infrastructure plan \
     -e TF_VAR_vault_ami=ami-01742db1d536b4980

I have noticed that this could cause minimal downtime, but I have built the terraform setup so that even without a load balancer, it ensures that the old VM is destroyed only when the new one is ready5. 🙃

If something seems broken, I can always re-deploy to the previous image and rollback to the old version:

make -C infrastructure plan \
     -e TF_VAR_vault_ami=ami-0894b635d1bd24710

Automation with GitLab

Due to lack of time I was able to automate using GitLab CI/CD Pipelines a set of tools and not being able to chain them.

For example, it is possible to have the Pipeline automated so that after a Merge Request is created, terraform will apply the changes to a new environment. The Packer setup can be automated to build a new image periodically so that Terraform can automagically fillter the AMI IDs and find the latest one5.

The current automation takes care of renewing a Vault token that has specific policies for GitLab CI/CD public pipeline runners, but every month it can build a new Vault AMI automagically.


Is it worth it? Have I achieved the goals? YES 🤔

The VM has limited attack surface by limiting the access to it as well as locking it down as much as possible. I can test and validate new versions and rollback to the previous version anytime if I need to. This is perfect for Vault!

Should I start using Immutable Infrastructure everywhere? Maybe

I would use Immutable Infrastructure to deploy Kubernetes minions, Nomad clients or Cockroach nodes, but after this I will not replace docker containers with VMs! The main reason is that it is not scaling quickly as when scaling vertically. Running upgrades of a full OS is definitely way less efficient than simply upgrading to a different docker container. I would use Immutable Infrastructure to deploy Hosts of multi-tenants platforms so that the services can scale vertically with a scheduler while the hosts can scale horizontally with the cloud provider and reduce downtimes.

While exploring it, I have discovered that some of my goals are actually harder without IaC tools. The process requires automation, but after a little, the benefits are clear, and I will keep using this to deploy services when required but not always. I see SREs and DevOps Engineers having their life simplified by using Immutable Infrastructure on their platforms but not more than that.

Yeah, it was worth it

That said, I think I learned what is really important: prevent humans from making mistakes by automating the hell out of it. 🤪

If you want to explore more, you can read the following articles:

  1. This allows Blue/Green deployments even with VM and can help to reduce or avoid any downtime. ↩︎

  2. Vault requires some manual operation (unsealing). anyway it is possible to explore a feature that will automatically unseal by using AWS KMS (or similar on GPC / Azure) Due to time constraints, I am not exploring this feature that is needed for autoscaling. In any case if this was a simpler project it would have not been a problem. ↩︎

  3. Due to the nature of Vault, we need to unseal it manually. The service will be reachable but the secrets will be locked. This can be automated2 ideally with a KMS solution. ↩︎

  4. Unless the human error is written down as a script. 😅 ↩︎

  5. But I was running out of time to do it 😅 (Or maybe I am just lazy) ↩︎

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