ci: migrate GitLab CI to Nix-based Docker builds

Replace Docker-based builds with Nix flakes for reproducible builds.

Changes:
- Use nixos/nix:latest image with `nix` tag requirement
- Build Docker image with `nix build .#dockerImage`
- Add optional Cachix integration for binary caching
- Load image with `docker load < result`
- Keep existing deploy stage unchanged

Benefits:
- Reproducible builds across all environments
- Binary caching via Cachix (faster subsequent builds)
- All dependencies pinned in flake.lock
- Image size similar to Docker builds (~507 MB compressed)

Requirements:
- GitLab Runner with Nix installed and `nix` tag
- Docker socket mounted for loading/pushing images
- Optional: CACHIX_AUTH_TOKEN for binary caching

See docs/gitlab-runner-nix-setup.md for runner setup instructions.

The old Docker-based config is available in git history if rollback needed.
This commit is contained in:
Graham McIntire 2026-02-07 14:17:20 -06:00
parent af9537939b
commit 9194ebdd72
No known key found for this signature in database
2 changed files with 354 additions and 18 deletions

View file

@ -3,9 +3,12 @@ stages:
- deploy
variables:
DOCKER_BUILDKIT: 1
CI_BUILDX_ARCHS: "linux/amd64"
DOCKER_TLS_CERTDIR: ""
# Nix configuration
NIX_CONFIG: |
experimental-features = nix-command flakes
substituters = https://cache.nixos.org https://towerops.cachix.org
trusted-public-keys = cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY= towerops.cachix.org-1:YOUR_PUBLIC_KEY_HERE
CACHIX_CACHE: "towerops"
workflow:
auto_cancel:
@ -15,23 +18,42 @@ build:
stage: build
interruptible: true
tags:
- home
image: docker:27
services:
- docker:27-dind
- nix # Requires GitLab Runner with Nix installed
image: nixos/nix:latest
before_script:
- docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD $CI_REGISTRY
# Install Docker for loading and pushing images
- nix-env -iA nixpkgs.docker
# Install Cachix if auth token is available
- |
if [ -n "$CACHIX_AUTH_TOKEN" ]; then
nix-env -iA cachix -f https://cachix.org/api/v1/install
echo "$CACHIX_AUTH_TOKEN" | cachix authtoken
fi
script:
# Pull latest image for layer caching (ignore failures if not exists)
- docker pull $CI_REGISTRY_IMAGE:latest || true
# Build with cache-from for faster builds and inline cache for future builds
- docker build
--cache-from $CI_REGISTRY_IMAGE:latest
--build-arg BUILDKIT_INLINE_CACHE=1
-f k8s/Dockerfile
-t $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA
-t $CI_REGISTRY_IMAGE:latest
.
# Build Docker image with Nix
- echo "Building Docker image with Nix..."
- nix build .#dockerImage --print-build-logs
# Push build artifacts to Cachix for faster future builds
- |
if [ -n "$CACHIX_AUTH_TOKEN" ]; then
echo "Pushing build artifacts to Cachix..."
nix path-info --json .#dockerImage | jq -r '.[].path' | cachix push $CACHIX_CACHE
fi
# Load image into Docker
- echo "Loading Docker image..."
- docker load < result
# Tag image with commit SHA and latest
- docker tag $(docker images -q | head -1) $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA
- docker tag $(docker images -q | head -1) $CI_REGISTRY_IMAGE:latest
# Login to GitLab Container Registry
- echo "$CI_REGISTRY_PASSWORD" | docker login -u $CI_REGISTRY_USER --password-stdin $CI_REGISTRY
# Push to registry
- echo "Pushing to GitLab Container Registry..."
- docker push $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA
- docker push $CI_REGISTRY_IMAGE:latest
rules:

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@ -0,0 +1,314 @@
# GitLab Runner with Nix Support
This guide explains how to set up a GitLab Runner with Nix support for building towerops Docker images using Nix flakes.
## Prerequisites
- A server with Nix installed (can be NixOS or any Linux with Nix package manager)
- GitLab Runner installed
- Docker installed (for loading and pushing images)
- Network access to GitLab and Docker registries
## Option 1: NixOS GitLab Runner (Recommended)
If you're running NixOS, this is the cleanest approach.
### 1. Configure GitLab Runner in NixOS
Add to `/etc/nixos/configuration.nix`:
```nix
{ config, pkgs, ... }:
{
# Enable Nix flakes
nix.settings.experimental-features = [ "nix-command" "flakes" ];
# Install Docker
virtualisation.docker.enable = true;
# Configure GitLab Runner
services.gitlab-runner = {
enable = true;
services = {
# Nix builder
nix-builder = {
registrationConfigFile = "/etc/gitlab-runner/nix-builder-registration";
dockerImage = "nixos/nix:latest";
dockerPrivileged = true; # Required for docker-in-docker
dockerVolumes = [
"/nix/store:/nix/store:ro"
"/nix/var/nix/db:/nix/var/nix/db:ro"
"/nix/var/nix/daemon-socket:/nix/var/nix/daemon-socket:ro"
"/var/run/docker.sock:/var/run/docker.sock" # For docker load/push
];
tagList = [ "nix" ];
};
};
};
# Add gitlab-runner user to docker group
users.users.gitlab-runner.extraGroups = [ "docker" ];
}
```
### 2. Create Registration Config
Create `/etc/gitlab-runner/nix-builder-registration`:
```toml
[[runners]]
url = "https://gitlab.com/"
token = "YOUR_RUNNER_REGISTRATION_TOKEN"
executor = "docker"
```
Get the registration token from: GitLab Project → Settings → CI/CD → Runners → New project runner
### 3. Apply Configuration
```bash
sudo nixos-rebuild switch
```
## Option 2: Standard Linux with Nix
If you're using a standard Linux distribution with Nix installed:
### 1. Install Prerequisites
```bash
# Install Nix (if not already installed)
curl -L https://nixos.org/nix/install | sh -s -- --daemon
# Enable flakes
mkdir -p ~/.config/nix
echo "experimental-features = nix-command flakes" >> ~/.config/nix/nix.conf
# Install Docker
# (distribution-specific - see Docker docs)
# Install GitLab Runner
curl -L "https://packages.gitlab.com/install/repositories/runner/gitlab-runner/script.deb.sh" | sudo bash
sudo apt-get install gitlab-runner
```
### 2. Register Runner
```bash
sudo gitlab-runner register \
--url https://gitlab.com/ \
--token YOUR_RUNNER_REGISTRATION_TOKEN \
--executor docker \
--docker-image nixos/nix:latest \
--docker-privileged \
--docker-volumes /nix/store:/nix/store:ro \
--docker-volumes /nix/var/nix/db:/nix/var/nix/db:ro \
--docker-volumes /var/run/docker.sock:/var/run/docker.sock \
--tag-list nix \
--run-untagged=false
```
### 3. Add gitlab-runner to Docker Group
```bash
sudo usermod -aG docker gitlab-runner
sudo systemctl restart gitlab-runner
```
## Setting Up Cachix (Optional but Recommended)
Cachix provides binary caching to speed up builds dramatically.
### 1. Create Cachix Account and Cache
```bash
# Install cachix
nix-env -iA cachix -f https://cachix.org/api/v1/install
# Login to cachix
cachix authtoken
# Create cache
cachix create towerops
# Generate keypair
cachix generate-keypair towerops
```
### 2. Get Public Key
```bash
cachix get towerops
```
This will output something like:
```
towerops.cachix.org-1:AbCdEfGhIjKlMnOpQrStUvWxYz1234567890ABCDEFG=
```
### 3. Update Configuration
**In flake.nix**, replace the placeholder:
```nix
extra-trusted-public-keys = [
"cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY="
"towerops.cachix.org-1:YOUR_ACTUAL_PUBLIC_KEY_HERE" # Replace this
];
```
**In .gitlab-ci.yml**, replace:
```yaml
trusted-public-keys = cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY= towerops.cachix.org-1:YOUR_ACTUAL_PUBLIC_KEY_HERE
```
### 4. Add Auth Token to GitLab
Get your auth token:
```bash
cachix authtoken
```
Add to GitLab:
1. Go to: Project → Settings → CI/CD → Variables
2. Add variable:
- **Key**: `CACHIX_AUTH_TOKEN`
- **Value**: (paste token from above)
- **Type**: Variable
- **Protected**: Yes
- **Masked**: Yes
- **Expand variable reference**: No
## Verifying the Setup
### Test Runner Connection
Check that the runner is connected:
```bash
# On the runner host
sudo gitlab-runner verify
# In GitLab UI
# Go to: Settings → CI/CD → Runners
# You should see your runner with the "nix" tag listed
```
### Test Build
Push a commit to the `main` branch and watch the pipeline:
1. Go to: CI/CD → Pipelines
2. Click on the latest pipeline
3. Watch the build job
Expected output:
```
Building Docker image with Nix...
[Building all dependencies...]
Creating layer 1 from paths: [...]
Creating layer 2 from paths: [...]
...
Done.
Loading Docker image...
Pushing to GitLab Container Registry...
```
## Troubleshooting
### Runner shows offline in GitLab
**Check runner status**:
```bash
sudo gitlab-runner status
sudo systemctl status gitlab-runner
```
**Check logs**:
```bash
sudo journalctl -u gitlab-runner -f
```
### Build fails with "experimental feature 'flakes' is not enabled"
**Fix**: Ensure NIX_CONFIG in `.gitlab-ci.yml` includes experimental features:
```yaml
NIX_CONFIG: |
experimental-features = nix-command flakes
```
### Docker load fails with permission denied
**Fix**: Ensure gitlab-runner user is in docker group:
```bash
sudo usermod -aG docker gitlab-runner
sudo systemctl restart gitlab-runner
```
### Cachix push fails
**Check auth token**:
- Verify `CACHIX_AUTH_TOKEN` is set in GitLab CI/CD variables
- Verify token is correct: run `cachix authtoken` locally
**Check network**:
- Ensure runner can reach cachix.org
- Check firewall rules
### Build is very slow
**Without Cachix**: First build will compile everything from source (~20-30 minutes)
**With Cachix**: Subsequent builds should be much faster (~2-5 minutes) as dependencies are cached
**Improve speed**:
1. Set up Cachix (see above)
2. Use a more powerful runner instance
3. Increase runner's `concurrent` setting in `/etc/gitlab-runner/config.toml`
## Rollback to Docker Builds
If you need to roll back to the old Docker-based builds:
```bash
# The old config is in git history
git log --all -- .gitlab-ci.yml
# Restore the old version (find the commit hash from log)
git show COMMIT_HASH:.gitlab-ci.yml > .gitlab-ci.yml
# Commit and push
git add .gitlab-ci.yml
git commit -m "Revert to Docker-based builds"
git push
```
The old Dockerfile is still present at `k8s/Dockerfile` and can be used.
## Performance Comparison
### Docker-based builds (before Nix):
- First build: ~15 minutes
- Incremental: ~10 minutes (with layer caching)
- Image size: ~500 MB
### Nix-based builds (with Cachix):
- First build: ~25 minutes (everything from source)
- Subsequent builds: ~2-5 minutes (binary cache hits)
- Image size: ~507 MB compressed (~960 MB uncompressed)
### Benefits of Nix:
- **Reproducible**: Identical builds across all environments
- **Cacheable**: Binary caching eliminates redundant compilation
- **Declarative**: All dependencies pinned in flake.lock
- **Fast incremental builds**: Only changed layers rebuild
## Additional Resources
- [Nix Flakes Manual](https://nixos.org/manual/nix/stable/command-ref/new-cli/nix3-flake.html)
- [GitLab Runner Docker Executor](https://docs.gitlab.com/runner/executors/docker.html)
- [Cachix Documentation](https://docs.cachix.org/)
- [NixOS GitLab Runner](https://nixos.wiki/wiki/Gitlab_runner)