Getting Started with LiteFS in Docker

Overview

This guide will walk you through the steps of getting a LiteFS cluster up and running using Docker. You can also use this guide as a reference for running LiteFS on a Linux server with minimal changes. If you’re planning to run your app on Fly.io, please take a look at Getting Started with LiteFS on Fly.io instead.

For a full, working example of a LiteFS application, with a docker-compose setup that you can run locally, please see the litefs-example repository.

Adding LiteFS to your Dockerfile

Dependencies

The litefs binary is self-contained, but you’ll need to install the fuse3 library so LiteFS is able to mount a local file system. You’ll also need ca-certificates if you’re connecting to Consul, and you’ll almost certainly want to install sqlite. This installation depends on your package manager, but here is a line you can add to your Dockerfile for alpine-based or debian-based images:

# for alpine-based images
RUN apk add ca-certificates fuse3 sqlite

# for debian/ubuntu-based images
RUN apt-get update -y && apt-get install -y ca-certificates fuse3 sqlite3

Installing LiteFS

LiteFS is meant to run inside your container alongside your application. You can pull in the litefs binary by copying it from the official Docker image:

COPY --from=flyio/litefs:0.5 /usr/local/bin/litefs /usr/local/bin/litefs

It’s recommended that you run LiteFS as root in Docker instead of using the USER command to change users. If you need to run your application as another user, use the su command to run your application as a non-root user.

Take a look at the example Dockerfile in the litefs-example repo for an example.

Configuring LiteFS

Most configuration options for LiteFS are set via a YAML configuration file called litefs.yml. This file is typically placed in /etc/litefs.yml but you can change the path by using the -config flag.

You can take a look at a complete example of what your litefs.yml file should look like.

File system

Let’s first set two fields to tell LiteFS where to mount its file system and where to store its internal data.

# This directory is where your application will access the database.
fuse:
  dir: "/litefs"

# This directory is where LiteFS will store internal data.
# You must place this directory on a persistent volume.
data:
  dir: "/var/lib/litefs"

Lease configuration

LiteFS only allows a single node to be the primary at any given time. The primary node is the only one that can write data to the database. The other nodes are called replicas and they provide a read-only copy.

The primary is determined by using a distributed lease. In this guide, we’ll be using a static lease, because it’s simple to configure.

You’ll need two slightly different configurations for your primary and replica nodes. In particular, use lease.candidate: true in the primary node configuration, and lease.candidate: false in the replica node configuration. Here’s an example of the primary node’s litefs.yml file:

lease:
  # Required. Must be either "consul" or "static".
  type: "static"

  # Required. The URL for the primary node's LiteFS API.
  # Note: replace `primary` with the appropriate hostname for your primary node!
  advertise-url: "http://primary:20202"

  # Specifies whether the node can become the primary. If using
  # "static" leasing, this should be set to true on the primary
  # and false on the replicas.
  # Note: update this to `false` on the replica nodes!
  candidate: true

The replica node configuration should be identical, except with lease.candidate set to false.

Running LiteFS

The main command used to start LiteFS is the litefs mount command. This mounts a FUSE file system and then starts an API server for LiteFS nodes to communicate with each other. You can use this as the ENTRYPOINT in your Dockerfile:

ENTRYPOINT litefs mount

Running as a supervisor

LiteFS can either be run on its own or it can act as a simple supervisor process for your application. Running as a supervisor lets LiteFS wait to start the application until after it has connected to the cluster.

You can specify one or more commands in the exec section of your config. If you set lease.promote to true, then you can specify to run your migration scripts only on candidate nodes. This means that candidates will automatically promote to the primary and run the migrations.

exec:
  # Only run migrations on candidate nodes.
  - cmd: "rails db:migrate"
    if-candidate: true

  # Then run the application server on all nodes.
  - cmd: "rails server"

Docker container privileges

LiteFS uses the FUSE filesystem, which requires some additional privileges to run. The easiest way to get this working quickly is to run with --privileged:

docker run --privileged ...

Depending on your security requirements, you should take a look at the FUSE documentation and decide whether you can reduce privileges!

Testing your LiteFS instance

Once LiteFS is mounted, you can use SQLite clients or the sqlite3 CLI to interact with databases on the mount directory:

sqlite3 /litefs/my.db

LiteFS only allows files in the root of the mount and it does not currently support subdirectories.

Importing your database

If you have an existing database, you can import it using the litefs import command.

litefs import -name my.db /path/to/database

Refer to the litefs import documentation for more details.

Configuring writes to primary node

LiteFS has a few differences from regular SQLite since it is a distributed system. LiteFS requires that all writes occur on the primary node which means that applications need to redirect write requests to the current primary. It’s also possible to issue a write to the primary and then read from a replica before the change is propagated to that replica.

For most web applications, you can take advantage of load balancer configuration to route writes to the primary node, assuming your application follows the convention of avoiding write operations (INSERT, UPDATE, etc.) on GET requests.

You can take a look at this sample nginx config which routes writes to the primary node, and load balances between primary and replica node for other requests.

Next steps

Back up your LiteFS cluster.