Podman Task Driver

Name: podman

Homepage: https://github.com/pascomnet/nomad-driver-podman

The podman task driver plugin for Nomad uses the Pod Manager (podman) daemonless container runtime for executing Nomad tasks. Podman supports OCI containers and its command line tool is meant to be a drop-in replacement for Docker's.

See the project's homepage for details.

Client Requirements

• Linux host with podman installed.
• nomad-driver-podman binary in Nomad's plugin_dir.

You need a varlink enabled podman binary and a system socket activation unit, see https://podman.io/blogs/2019/01/16/podman-varlink.html.

Since the Nomad agent, nomad-driver-podman plugin binary, and podman will reside on the same host, skip the ssh aspects of the podman varlink documentation above.

Task Configuration

Due to Podman's similarity to Docker, the example job created by nomad init -short is easily adapted to use Podman instead:

job "example" {
  datacenters = ["dc1"]

  group "cache" {
    task "redis" {
      driver = "podman"

      config {
        image = "docker://redis:3.2"

        port_map {
          db = 6379
        }
      }

      resources {
        cpu    = 500
        memory = 256

        network {
          mbits = 10
          port  "db"  {}
        }
      }
    }
  }
}

• image - The image to run.

config {
  image = "docker://redis"
}

• command - (Optional) The command to run when starting the container.

config {
  command = "some-command"
}

• args - (Optional) A list of arguments to the optional command. If no command is specified, the arguments are passed directly to the container.

config {
  args = [
    "arg1",
    "arg2",
  ]
}

• volumes - (Optional) A list of host_path:container_path strings to bind host paths to container paths.

config {
  volumes = [
    "/some/host/data:/container/data"
  ]
}

• tmpfs - (Optional) A list of /container_path strings for tmpfs mount points. See podman run --tmpfs options for details.

config {
  tmpfs = [
    "/var"
  ]
}

• hostname - (Optional) The hostname to assign to the container. When launching more than one of a task (using count) with this option set, every container the task starts will have the same hostname.

• init - Run an init inside the container that forwards signals and reaps processes.

config {
  init = true
}

• init_path - Path to the container-init binary.

config {
  init = true
  init_path = "/usr/libexec/podman/catatonit"
}

• user - Run the command as a specific user/uid within the container. See task configuration.

• memory_reservation - Memory soft limit (unit = b (bytes), k (kilobytes), m (megabytes), or g (gigabytes))

After setting memory reservation, when the system detects memory contention or low memory, containers are forced to restrict their consumption to their reservation. So you should always set the value below --memory, otherwise the hard limit will take precedence. By default, memory reservation will be the same as memory limit.

config {
  memory_reservation = "100m"
}

• memory_swap - A limit value equal to memory plus swap. The swap limit should always be larger than the memory value.

Unit can be b (bytes), k (kilobytes), m (megabytes), or g (gigabytes). If you don't specify a unit, b is used. Set LIMIT to -1 to enable unlimited swap.

config {
  memory_swap = "180m"
}

• memory_swappiness - Tune a container's memory swappiness behavior. Accepts an integer between 0 and 100.

config {
  memory_swappiness = 60
}

Networking

Podman supports forwarding and exposing ports like Docker. See Docker Driver configuration for details.

Plugin Options

The podman plugin has options which may be customized in the agent's configuration file.

• volumes stanza:

  • enabled - Defaults to true. Allows tasks to bind host paths (volumes) inside their container.
  • selinuxlabel - Allows the operator to set a SELinux label to the allocation and task local bind-mounts to containers. If used with volumes.enabled set to false, the labels will still be applied to the standard binds in the container.

plugin "nomad-driver-podman" {
  config {
    volumes {
      enabled      = true
      selinuxlabel = "z"
    }
  }
}

• gc stanza:

  • container - Defaults to true. This option can be used to disable Nomad from removing a container when the task exits.

plugin "nomad-driver-podman" {
  config {
    gc {
      container = false
    }
  }
}

• recover_stopped - Defaults to true. Allows the driver to start and reuse a previously stopped container after a Nomad client restart. Consider a simple single node system and a complete reboot. All previously managed containers will be reused instead of disposed and recreated.

plugin "nomad-driver-podman" {
  config {
    recover_stopped = false
  }
}