flyctl no longer uses buildpacks for Golang

Fresh Produce
1

tl;dr When you run fly launch on a Golang app, we no longer use Buildpack gcr.io/paketo-buildpacks/go.

Instead we generate a Dockerfile for you.

why? We’ve seen users hit errors with the Go buildpack, and thought it was time to setup something a bit more opinionated for Fly. Your opinions are also welcome as well [pr here].

tweaking the Setup The good news if that if our opinions aren’t what you want, you can pretty easily change it (maybe you need CGO_ENABLED=1 or want to include ldflags).

The fly launch command will read your go.mod file and use the Go version set there. You can over-ride that in your fly.toml by adding build args:

# fly.toml
[build.args]
  GO_VERSION = "1.21.5"

As I’m writing this, the Dockerfile created looks something like this:

ARG GO_VERSION=1
FROM golang:${GO_VERSION}-alpine as builder

WORKDIR /usr/src/app
COPY go.mod go.sum ./
RUN go mod download && go mod verify
COPY . .
RUN go build -v -o /run-app .


FROM alpine:latest

COPY --from=builder /run-app /usr/local/bin/
CMD ["run-app"]
6 Likes
2

Is there a way to customize the build target, like there used to be with the BP_GO_TARGETS variable?

3

You should be able to edit the RUN go build -v -o /run-app . line in the generated Dockerfile to customize the build target.

4

This move out of buildpacks makes the job harder when having to deal with the Docker complexity:

  • how to configure a release_command? The Go project can generate two binaries, or one binary with arguments (for example “app web” and “app dbmigrate”)
  • how the binary can access source files, for instance to execute SQL files?

Any help would be much appreciated,
Thanks

5

Hey Simon,

You can set release command in the deploy section of your fly.toml.

[deploy]
  release_command = "bin/rails db:prepare"

how the binary can access source files, for instance to execute SQL files?

I’m not sure I follow what you’re asking here, the binary can access any source files you’ve added to your docker image by specifying location it’s been copied to. Could you give an example of what you’re trying to do?