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User’s Guide / Server administration / Instance configuration

Instance configuration

Instance configuration

For each Tarantool instance, you need two files:

  • [Optional] An application file with instance-specific logic. Put this file into the /usr/share/tarantool/ directory.

    For example, /usr/share/tarantool/my_app.lua (here we implement it as a Lua module that bootstraps the database and exports start() function for API calls):

    local function start()
        box.schema.space.create("somedata")
        box.space.somedata:create_index("primary")
        <...>
    end
    
    return {
      start = start;
    }
    
  • An instance file with instance-specific initialization logic and parameters. Put this file, or a symlink to it, into the /etc/tarantool/instances.enabled directory.

    For example, /etc/tarantool/instances.enabled/my_app.lua (here we load my_app.lua module and make a call to start() function from that module):

    #!/usr/bin/env tarantool
    
    box.cfg {
        listen = 3301;
    }
    
    -- load my_app module and call start() function
    -- with some app options controlled by sysadmins
    local m = require('my_app').start({...})
    

Instance file

After this short introduction, you may wonder what an instance file is, what it is for, and how tarantoolctl uses it. After all, Tarantool is an application server, so why not start the application stored in /usr/share/tarantool directly?

A typical Tarantool application is not a script, but a daemon running in background mode and processing requests, usually sent to it over a TCP/IP socket. This daemon needs to be started automatically when the operating system starts, and managed with the operating system standard tools for service management – such as systemd or init.d. To serve this very purpose, we created instance files.

You can have more than one instance file. For example, a single application in /usr/share/tarantool can run in multiple instances, each of them having its own instance file. Or you can have multiple applications in /usr/share/tarantool – again, each of them having its own instance file.

An instance file is typically created by a system administrator. An application file is often provided by a developer, in a Lua rock or an rpm/deb package.

An instance file is designed to not differ in any way from a Lua application. It must, however, configure the database, i.e. contain a call to box.cfg{} somewhere in it, because it’s the only way to turn a Tarantool script into a background process, and tarantoolctl is a tool to manage background processes. Other than that, an instance file may contain arbitrary Lua code, and, in theory, even include the entire application business logic in it. We, however, do not recommend this, since it clutters the instance file and leads to unnecessary copy-paste when you need to run multiple instances of an application.

tarantoolctl configuration file

While instance files contain instance configuration, tarantoolctl configuration file contains the configuration that tarantoolctl uses to override instance configuration. In other words, it contains system-wide configuration defaults.

Most of the parameters are similar to those used by box.cfg{}. Here are the default settings (installed to /etc/default/tarantool as part of Tarantool distribution):

default_cfg = {
    pid_file  = "/var/run/tarantool",
    wal_dir   = "/var/lib/tarantool",
    memtx_dir = "/var/lib/tarantool",
    vinyl_dir = "/var/lib/tarantool",
    log       = "/var/log/tarantool",
    username  = "tarantool",
}
instance_dir = "/etc/tarantool/instances.enabled"

where:

  • pid_file
    Directory for the pid file and control-socket file; tarantoolctl will add “/instance_name” to the directory name.
  • wal_dir
    Directory for write-ahead .xlog files; tarantoolctl will add “/instance_name” to the directory name.
  • memtx_dir
    Directory for snapshot .snap files; tarantoolctl will add “/instance_name” to the directory name.
  • vinyl_dir
    Directory for vinyl files; tarantoolctl will add “/instance_name” to the directory name.
  • log
    The place where the application log will go; tarantoolctl will add “/instance_name.log” to the name.
  • username
    The user that runs the Tarantool instance. This is the operating-system user name rather than the Tarantool-client user name. Tarantool will change its effective user to this user after becoming a daemon.
  • instance_dir
    The directory where all instance files for this host are stored. Put instance files in this directory, or create symbolic links.

As a full-featured example, you can take example.lua script that ships with Tarantool and defines all configuration options.