There are lots of posts about setting up CD with Jenkins and Kubernetes but I haven't found any describing how to do it with Nomad and Gitlab.

So here's how I did it…

I'm assuming that you've already got a working Gitlab (on premise) and Nomad cluster setup and that you've already got CI (continuous integration) working with them.

Getting this working isn't particularly difficult, the “trick” is to run a nomad command that loads an updated job file.

Overall steps are:

1. make a docker image with nomad in it
2. update your .nomad job file
3. update your project's .gitlab-ci.yml with a deploy step
4. go have a beverage

Docker in Docker build image

Keeping track of all the images when building can get a bit tricky…

I've made an “image builder” based on alpine linux that has docker in it. It's called ${docker_registry}/public/alpine:3 in the examples below.

If you already have a similar builder image then you can skip this step.

FROM gliderlabs/alpine

RUN apk add --update --no-cache docker make bash curl jq

docker build -t ${docker_registry}/public/alpine:3 -F Dockerfile .
docker push ${docker_registry}/public/alpine:3

or have an appropriate .gitlab-ci.yml do it for you.

Make nomad docker image

Make a new Gitlab project, in my case ops/nomad-deployer.

1. download nomad
2. make Dockerfile and .gitlab-ci.yml
3. git commit and git push all the things

Dockerfile

FROM alpine:3.9

RUN apk add --update --no-cache libc6-compat gettext
COPY nomad /usr/local/bin/nomad

.gitlab-ci.yml

variables:
  docker_registry: registry.example.com
  docker_image: public/nomad-deployer

stages:
  - build

build:
  stage: build
  image: ${docker_registry}/public/alpine:3
  script:
    - tag=${docker_registry}/${docker_image}:latest
    - echo "building and pushing tag $tag"
    - docker build --pull -t ${tag} -f Dockerfile .
    - docker push ${tag}

Update your project

And now for the fun part!

I'm assuming that you already have a .nomad file for your service in the current directory and it's called project.nomad. Update code below to match your situation.

The magic happens by having envsubst substitute CI_COMMIT_SHORT_SHA with the current git hash. You lose having a nice docker image version but gain not having to increment anything and always knowing exactly what code you're running.

project.nomad

job "project" {
  ...

  group "project" {
    ...

    task "project" {
      ...
      driver = "docker"

      config {
        image   = "registry.example.com/example/project:${CI_COMMIT_SHORT_SHA}"
        ...
      } # config
    } # task run
  } # group
} # job

.gitlab-ci.yml

At the time of writing there is an open bug where gitlab doesn't properly expand CI_PROJECT_NAME but once it's fixed replace project with ${CI_PROJECT_NAME} below for a more generic .gitlab-ci.yml.

1. change NOMAD_ADDR to match your situation
2. change all the variables actually…
3. feel free to delete line - cat job.nomad once everything is working
4. note line when: manual, that means you need to manually push a button in gitlab to deploy

variables:
  NOMAD_ADDR: http://hashi1.example.com:4646
  docker_registry: registry.example.com
  docker_image: example/project

stages:
  - build
  - test
  - deploy

build:
  stage: build
  image: ${docker_registry}/public/alpine:3
  script:
    - tag=${docker_registry}/${docker_image}:${CI_COMMIT_SHORT_SHA}
    - echo "building and pushing tag $tag"
    - docker build --pull -t ${tag} -f Dockerfile .
    - docker push ${tag}

test:
  stage: test
  ...

deploy:
  stage: deploy
  image: registry.example.com/public/nomad-deployer:latest
  script:
    - envsubst '${CI_COMMIT_SHORT_SHA}' < project.nomad > job.nomad
    - cat job.nomad
    - nomad validate job.nomad
    - nomad plan job.nomad || if [ $? -eq 255 ]; then exit 255; else echo "success"; fi
    - nomad run job.nomad
  environment:
    name: production
  allow_failure: false
  when: manual

bringing it all together

1. edit some sweet project code
2. git commit and git push it
3. open gitlab jobs url for your project
4. push the play button to deploy your new version

If you have great tests and want to auto deploy then change:

when: manual

to

only:
  - master

all done

Hopefully you've now got CD to accompany your CI.

Thanks to @henrikjohansen on https://gitter.im/hashicorp-nomad/Lobby for his code snippet that was the missing piece for me.