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crun-vm/docs/3-systemd.md

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3. Running VMs as systemd services

crun-vm also enables you to define a systemd service corresponding to a VM, and thus manage it through systemd. This relies on Podman's Quadlet feature, through which you can define systemd unit files for containers.

[!TIP]

This means that system containers and VMs can both be deployed and managed using the same tooling, i.e., systemd!

Here, we overview how you can create Quadlet-powered systemd services to manage VMs. Make sure you have installed both crun-vm and Podman (see 1. Installing crun-vm).

Navigation
  1. Installing crun-vm
  2. Running VMs with Podman or Docker
  3. Running VMs as systemd services
  4. Running VMs in Kubernetes
  5. crun-vm(1) man page

Creating a systemd service for a VM

The easiest way to do this is using Podlet, a tool that can generate a systemd unit file corresponding to a given podman-run command. (Follow the instructions at https://github.com/containers/podlet to install Podlet.) This means we can apply it to the podman-run commands we use to launch VMs.

For instance, say you're using this command to launch a VM that runs a web service (see 2. Running VMs with Podman or Docker to learn how crun-vm can be used with Podman):

$ podman run --runtime crun-vm --detach -p 8000:80 quay.io/crun-vm/example-http-server:latest

To convert this invocation into an equivalent systemd container unit definition, you would run:

$ podlet \
    --install \
    --wanted-by default.target \
    podman run --runtime crun-vm --detach -p 8000:80 quay.io/crun-vm/example-http-server:latest
#example-http-server.container
[Container]
Image=quay.io/crun-vm/example-http-server:latest
PublishPort=8000:80
GlobalArgs=--runtime crun-vm

[Install]
WantedBy=default.target

The --install, --wanted-by default.target options configure the service to run automatically on boot.

Finally, to actually install this unit definition, you would instead run (using sudo to become root):

$ sudo podlet \
    --name my-web-service \
    --unit-directory \
    --install \
    --wanted-by default.target \
    podman run --runtime crun-vm --detach -p 8000:80 quay.io/crun-vm/example-http-server:latest
Wrote to file: /etc/containers/systemd/my-web-service.container

$ systemctl daemon-reload  # load the new service

With this, your web server VM becomes a systemd service:

$ sudo systemctl status my-web-service
○ my-web-service.service
     Loaded: loaded (/etc/containers/systemd/my-web-service.container; generated)
    Drop-In: /usr/lib/systemd/system/service.d
             └─10-timeout-abort.conf
     Active: inactive (dead)

$ sudo systemctl start my-web-service  # start the service without having to reboot

$ sudo systemctl status my-web-service
● my-web-service.service
     Loaded: loaded (/etc/containers/systemd/my-web-service.container; generated)
    Drop-In: /usr/lib/systemd/system/service.d
             └─10-timeout-abort.conf
     Active: active (running) since Tue 2024-04-30 21:14:36 WEST; 4s ago
   Main PID: 1531707 (conmon)
      Tasks: 48 (limit: 76805)
     Memory: 1.1G (peak: 1.1G)
        CPU: 11.768s
[...]

$ curl localhost:8000
<!DOCTYPE HTML>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Directory listing for /</title>
</head>
<body>
[...]

Further information

See this article for additional information on Podman Quadlet, and the podman-systemd.unit(5) man page for the reference format of container unit files.

The podlet commands provides several options to further customize the generated container unit file. Run podlet -h to know more.