Deploying docker containers declaratively

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I went looking for this and still haven’t found much other than running a whole Kubernetes stack (which seems like a lot of work). My solution so far has been to write systemd units that manage a docker container, which has been working reasonably well. for instance:

  systemd.services.prometheus = {
    description = "Prometheus";
    wantedBy = [ "multi-user.target" ];
    after = [ "docker.service" "docker.socket" ];
    requires = [ "docker.service" "docker.socket" ];
    script = ''
      exec ${pkgs.docker}/bin/docker run \
          --rm \
          --name=prometheus \
          --network=host \
          -v ${./prometheus.yml}:/etc/prometheus/prometheus.yml \
          -v prometheus_data:/prometheus \
          prom/prometheus:v2.2.1 \
          "$@"
    '';
    scriptArgs = lib.concatStringsSep " " [
      "--config.file=/etc/prometheus/prometheus.yml"
      "--storage.tsdb.path=/prometheus"
      "--web.console.libraries=/usr/share/prometheus/console_libraries"
      "--web.console.templates=/usr/share/prometheus/consoles"
      "--storage.tsdb.retention=30d"
      "--web.external-url=https://example.com/prometheus"
      "--web.route-prefix=/"
    ];
    preStop = "${pkgs.docker}/bin/docker stop prometheus";
    reload = "${pkgs.docker}/bin/docker restart prometheus";
    serviceConfig = {
      ExecStartPre = "-${pkgs.docker}/bin/docker rm -f prometheus";
      ExecStopPost = "-${pkgs.docker}/bin/docker rm -f prometheus";
      TimeoutStartSec = 0;
      TimeoutStopSec = 120;
      Restart = "always";
    };
  };

(I know there’s a Prometheus module in NixOS; I wanted a newer version than was available at the time and this was a quick solution)

This could be generalized into a reusable module in the same general way as systemd.services.* to provide an interface vaguely like what currently exists in containers.* for systemd-nspawn containres.

Hopefully there’s a better way though; what I’ve got here works, but it’s not ideal.

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