lapis-systemd is a Lapis extension that lets you create systemd service files for your Lapis applications. It also provides a minimal module to work with the systemd journal.

$ luarocks install lapis-systemd

$ lapis systemd service --help
Usage: lapis systemd service ([--install] | [--print]) [-h]
       [<environment>]

Generate service file

Arguments:
   environment           Environment to generate service file for (overrides --environment)

Options:
   -h, --help            Show this help message and exit.
   --install             Installs the service file to the system, requires sudo permission
   --print, -p           Print the service file to stdout instead of writing it

The service command generates service files based on the environment configuration. From your shell:

$ lapis systemd service development

Will generate a file in the current directory, named after your app: some-app-development.service

The contents might look like this:

[Unit]
Description=some-app development
After=network.target

[Service]
Type=simple
PIDFile=/home/leafo/code/sites/itch.io/logs/nginx.pid
Environment='PATH=/home/leafo/.luarocks/bin:/usr/bin' 'LUA_PATH=;;/home/leafo/.luarocks/share/lua/5.1/?.lua;/home/leafo/.luarocks/share/lua/5.1/?/init.lua' 'LUA_CPATH=;;/home/leafo/.luarocks/lib/lua/5.1/?.so'
WorkingDirectory=/home/leafo/code/sites/itch.io
ExecStart=/home/leafo/.luarocks/bin/lapis server development
ExecReload=/home/leafo/.luarocks/bin/lapis build development

[Install]
WantedBy=multi-user.target

By default, service command will copy certain environment variables from the current shell and embed them directly into the service file. This ensures that Lapis is run as if you had launched it directly from your shell. The following environment variables are embedded by default:

• PATH
• LUA_PATH
• LUA_CPATH

Because of these hard-coded paths, it is not recommended to check the generated service files into your repository. If you ever move the project or reconfigure your system, you should regenerate the service file.

You can generate and install the service file to the system using the following command:

$ lapis systemd service development --install

Do not run this command with sudo, as it will invoke sudo for you when copying the necessary file. Executing it with sudo could result in a service file with incorrect environment variables embedded

You can then start your service:

$ sudo systemctl start some-app-development

And view the logs for it:

$ sudo journal -u some-app-development

The service file is configured from the systemd block within your Lapis configuration. This simplifies the generation of a service file based on the environment using a single, consistent command.

The user option specifies the user under which the service will run. This can be particularly useful if you need the service to have specific permissions that are associated with a certain user.

If the user option is not provided, the service will not specify a user will run under the default user of the system.

In the configuration example below, the service will run as the user "leafo".

-- config.lua
local config = require("lapis.config")

config("production", {
  systemd = {
    user = "leafo" -- service will run as user
  }
})

If user is set to true, the name of the current user will be used. Note that the user is embedded into the service file at the time of its creation and is not dynamically determined at runtime. The user is determined via whoami at the time of the service file's generation.

The env option allows you specify the environment variables for the service. The value of env can either be a string, a table, or a boolean.

By default systemd service files have a minimal PATH and no other environment variables set. Any environment variables that are needed by your application should be assigned in the service file.

If env is not set, it will default to copying the environment variables "PATH", "LUA_PATH", "LUA_CPATH". To avoid this default behavior set env to false to skip setting environment variables in the service file, or manually specify the value:

If env is a table, it can contain two types of entries, each representing how to set the environment variable:

• Array entries: These are treated as names of environment variables that should be copied from the current shell environment.
• Key-value pairs: These represent environment variables that should be set directly, with the key as the variable name and the value as the variable value.

(If env is a string, it is considered used as a single name of the environment variable to copy)

For example:

If you want to set the environment variable PORT to 8080 and copy the environment variable DATABASE_URL, you could use the following configuration:

-- config.lua
local config = require("lapis.config")

config("production", {
  systemd = {
    env = {
      PORT = 8080,
      "DATABASE_URL"
    }
  }
})

The name option allowed for manual control of the name of the systemd service.

If not set, the name is auto-generated from the last part of the current directory name. For example, /home/user/my-app would default to my-app.

The dir option sets the service's working directory. If not set, it defaults to the directory at the service file's generation time using pwd.

The lapis_bin option sets the location of the Lapis executable. If not set, it defaults to the location returned by the command which lapis.

You can access the systemd journal with the lapis.systemd.journal module:

journal = require("lapis.systemd.journal")
journal.log("hello world!", {priority = 5})

Note this will only work if the journal config option is set to a truthy value.

The log method will be a no-op unless the journal config option is set to a truthy value. This will allow you to conditionally write to the journal based on the Lapis environment.

-- config.lua
local config = require("lapis.config")

config("production", {
  systemd = {
    journal = true
  }
})

This will loop forever listening for new log messages.

local j = require("lapis.systemd.journal")

for entry in j.listen() do
  print("Got entry:")
  for k, v in pairs(entry) do
    print(""k k,v)
  end
end