Sqlite Migrations with Golang on Fly.io

6 September 2022

I’ve been developing a simple RSS reader in Go. Usually, for a small personal project like this, I’d use Heroku for a fast simple deployment. But with Heroku’s free tier being sunset, I’ve been looking for a replacement platform. I came to choose between two options:

  1. Render
  2. Fly.io

I’m pretty cheap, so for a toy app like this, I only considered free options. I don’t need much compute but I do need some form of persistent storage. Both of these platforms have free PostgreSQL offerings but Fly.io’s is much better. On the free plan, Render will delete your data after 90 days. On the other hand Fly.io offers up to 3GB of persistent volume storage. Although I used PostgreSQL as a measurement for which provider to choose, I ultimately didn’t use PostgreSQL.

Developing locally with Sqlite is a breeze. The developer experience of having the entire database being a single file is too easy to pass up. After my initial prototype, I considered switching the database to PostgreSQL. This wouldn’t have been too difficult with Go’s (more or less) database agnostic database/sql library but I decided against it so I could maintain my simple local development workflow.

Setting up a Sqlite database on Fly.io is pretty easy. First I needed to create a persistent volume. Here, I’m creating a volume called “database” with a size of 1GB (the largest size available in the free tier.)

fly volumes create database --size 1

Next, I can mount my volume on my app by adding the following to the fly.toml.


Now, I can point my app to use this volume to create it’s Sqlite database.

package main

import "database/sql"

func main() {
  db, err := sql.Open("sqlite3", "/mnt/database/rss-server.sqlite")
  // ...

Now our data will persist across deployments.


To deploy my app, I can either build my app with Fly.io’s provided build pack or write my own Dockerfile. Initially, I went with the build pack since that seemed like the simplest and quickest thing to do. I got my app built and deployed by running a single CLI command.

flyctl launch

But after the deployment, attempting to ping the server returned this error:

no such table: rss_feeds

It seems that I overlooked that my Sqlite database hasn’t been migrated yet!

For local development, I’ve been using golang-migrate/migrate as a library to write a migration binary. This works fine locally since I have my SQL files contained within the local repo but it starts to fall apart for the build pack. With the build pack, I can only deploy the single RSS server binary. Luckily, Fly.io allows you to write your own Dockerfile for deployments.

With my own Dockerfile, I now had a couple of choices to perform the migration:

  1. Package the Sqlite binary in my Dockerfile to run the migration SQL files.
  2. Package golang-migrate/migrate’s CLI application to run the migrations.
  3. Package the migration binary I’ve been using locally along with my SQL migration files.

I went with the third option as this is what was closet to my local development work flow. Adding a second binary along with the migration SQL files was easy to do with a builder image.

# syntax=docker/dockerfile:1
FROM golang:1.19-alpine as builder
WORKDIR /opt/rss-server/
# add gcc for CGO
RUN apk add build-base
COPY . .
# build the main rss-server binary
RUN go build
# build the migration binary
RUN go build -o migrate cmd/migrate/main.go

FROM alpine:latest
# copy over the binaries we built in the last step
COPY --from=builder /opt/rss-server/rss-server ./
COPY --from=builder /opt/rss-server/migrate ./
# don't forget to copy over the SQL migration files.
COPY --from=builder /opt/rss-server/db/migrations ./db/migrations
CMD ["./rss-server"]

With all that done, after a deployment, I can perform the migration by SSH-ing into the running container and running my migration binary.

flyctl ssh console -C "/opt/migrate"

One issue I see with using Sqlite is that I may have some difficulty extracting my data down the road. There’s currently no way for me to get my Sqlite database off of Fly.io. I’d imagine, since SSH is possible, that SCP should be possible too but there’s currently no indication in the docs. Fly.io is still pretty new so they might address this later down the line. Since this is still just a toy app, I’m not too concerned.

The whole experience of deploying my app was very easy. Fly.io’s flyctl CLI makes it easy to make updates to my app. Everything feels pretty close to the simple developer experience of git push heroku main. I especially liked that I could build my own Docker image. In the future, I can see myself continuing to use Fly.io to deploy small personal projects.