Deploying from Hydra with Terraform

[grahamc]

Description

It'd be slick to implement the concepts from https://determinate.systems/posts/hydra-deployment-source-of-truth in Terraform.

Specifically:

• Get the build information for a job's latest successful build, and latest successful build from a completed evaluation
• Get information about a specific constituent of an aggregate job

New or Affected Resource(s)

data "hydra_job"
data "hydra_job_aggregate_constituent"

Potential Terraform Configuration

Deploying from a job:

data "hydra_job" "latest_myapp" {
    project = "myapp"
    jobset = "main"
    job = "myapp"
    wait_for_all_jobs = true # latest-successful ... consider a better name?
}

resource "aws_instance" "web" {
  # ...

  provisioner "remote-exec" {
    command = "nix-env -p /nix/var/nix/profiles/myapp --set '${data.hydra_job.latest_myapp.outputs.out.path}'"
  }
}

Deploy the constituent of an aggregate job:

data "hydra_job_aggregate_constituent" "serverconfig" {
    project = "myapp"
    jobset = "main"
    job = "release_gate"
    constituent = "serverconfig"
    wait_for_all_jobs = true
}

resource "aws_instance" "web" {
  # ...

  provisioner "remote-exec" {
    inline = [
      "nix-env --profile /nix/var/nix/profiles/system --set '${data.hydra_job_aggregate_constituent.serverconfig.outputs.out.path}'",
      "/nix/var/nix/profiles/system/bin/switch-to-configuration switch",
    ]
  }
}

References

• Example: https://determinate.systems/posts/hydra-deployment-source-of-truth
• Improving the constituents API: The Constituents API is Awkward NixOS/hydra#1046