Albatros

A lightweight and (quasi-)stateless CI built on top of Nomad. Our main principle: offload as much work to Nomad as possible. We don't want to build an abstraction on top of it and hide Nomad internals, but instead expose them as directly and transparently as possible, so that you can benefit from all the features of this software. Albatros is a specialized CI for Nomad

When we can't offload our work directly to Nomad, we should consider offloading it to Gitea, Consul, and the others. At a last resort, we might do it in Albatros...

Deploy

Requirements: Nomad, Consul, Gitea

Prepare your nomad cluster:

nomad namespace apply -description "Continuous Integration" ci
nomad run hcl/builder.hcl

Run from the terminal directly:

export ALBATROS_URL="https://albatros.deuxfleurs.fr" 
export NOMAD_ADDR=...
export NOMAD_CLIENT_CERT=...
export NOMAD_CLIENT_KEY=...
export NOMAD_CACERT=...
export CONSUL_HTTP_ADDR=...
export CONSUL_CLIENT_CERT=...
export CONSUL_CLIENT_KEY=...
export CONSUL_CACERT=...
./albatros

Run from docker:

docker run --rm -it dxflrs/albatros:xxx

where xxx is the commit sha you want.

Bring Your Own Builder

One aspect that I don't like with traditional CI is that the way you can configure builds is very constrained by the vendor implementation choices. Like it or not, but Albatros has very few constraints in term of what build infrastructure should look like:

• It must be a Nomad parameterized job
• Your job must accept four mandatory meta parameters: REPO_URL, COMMIT, BRANCH, FLAVOR
• Your job may receive a payload containing the secrets stored in your job definition (subject to change)
• It must have have a task group named runner and, inside this group, a task named executor

And... that's basically all you need.

A NixOS builder with local cache

The nix builder will create a local cache on your node agent at /var/cache/albatros. It will create two folders: /var/cache/albatros/nix that contains a nix store, and /var/cache/albatros/cacheroot that contains nix roots, ie. the builds we must keep.

Caching is handled thanks to these roots: roots that are older than 7 days will be removed, then a garbage collection will be triggered, and their associate content will be deleted.

To keep your cache between builds, you must put your outlink in /mnt/cacheroot with a unique name. The git commit is a good candidate:

# create an output link at a persisted path
nix build --out-link $GCROOT

Register a build

Add to Consul a key in albatros hierarchy named after your repo URL as base64. Example:

albatros/aHR0cHM6Ly9naXQuZGV1eGZsZXVycy5mci9xdWVudGluL2FsYmF0cm9zLmdpdA==

The key must contain a JSON file with your desired token, gitea info, trust conditions, and secrets:

{
  "hook": {
    "token": "s3cr3t"
  },
  "gitea": {
    "url": "https://git.deuxfleurs.fr",
    "token": "c0ffee..."
  },
  "trusted": {
    "senders": [ "quentin", "lx" ]
  },
  "inject": "SECRET1=xx\nSECRET2=yy"
}

Register an access token if Gitea for your Albatros by creating an application token. The URL is /user/settings/applications. Name your app albatros for example, the token will be displayed once in light blue. Put it in the JSON file.

Your secret will be injected in your build environment only when trustig condition are matched. It wil be available in a dedicated file. Its path is communicated through an environment variable (see below). For now, we can only check that based on sender's login.

Then you can trigger a build as follow:

$ curl -d @example/albatros.json http://localhost:8080/hook?token=s3cr3t&flavor=default
builder/dispatch-1678866433-15aad86a

You need to pass your token, and you can optionally pass a flavor, that can be used later by your build script.

As you can see, you now have an identifier representing your job, you can use it to follow your logs (don't forget to urlencode it):

$ curl http://localhost:8080/build?job=builder%2Fdispatch-1678866433-15aad86a&log=stderr
+ go build
...

Of course, most of that will be handled by Gitea.

Writing your build script

You must create an executable .albatros file at the root of your repository. Then, you can use the interpreter you want to execute it, let use bash as an example, but please use python, javascript, or anything else that has proper error handling...

#!/usr/bin/env bash
echo "Building commit $COMMIT"
go build

During the build, the following environment variables are available:

REPO_URL=https://git.deuxfleurs.fr/quentin/albatros.git
COMMIT=3fff73597f8ca18ef04c0d9bf64132ba55aadcaa
BRANCH=main
FLAVOR=default
SECRET_PATH=/var/run/secrets/albatros/secret.txt

Security model

Albatros only tries to protect your secrets. To achieve that, we only inject them in the build script if the job has been sent (triggered) by a trusted sender. This decision is taken by looking at the webhook payload content.

To protect against sender impersonification, your webhook must be called only by trusted code, and more generally, your token must remain secret.

We assume otherwise that anyone can trigger the webhook through Gitea while replacing the content of the build script by a malicious software. Signing the build script is tempting but it will not prevent someone to put its malicious code, for example in a Rust project, in the build.rs file. So you must assume that your CI will execute untrusted code.

To protect against undesired code execution, you must harden your environment, for example by using VMs instead of containers, timeouts, and restricting some IO. All of that must be handled by Nomad. Also, be careful to the local network in which your workload will be executed.

Roadmap

Don't get me wrong, the 1.0 version is not ambitious at all and will have to few features for many of you. Still, I think it will be enough for us.

v1.0

See this v1.0 as a MVP that will serve Deuxfleurs needs, nothing more. Don't have any expectation in term of code quality, abstraction or anything else.

• Read Nomad+Consul config from environment variables
• Inject secrets only when the sender is trusted
• Test PR behavior

Ideas

Ideas are just... ideas. They are pure speculation, and if they are here, it means that will and time to implement them has not been found yet...

• Validate the gitea payload with hmac
• Refactor the code
• Register the builder programatically
• Allow users to define their own set of builders (ones with more CPU+RAM, etc.)
• Allow users to choose their image/rootfs
• Make Gitea optional
• Your idea