Something wrong with docker path in my build

Questions / Help Build debugging
1

Hello there, the fact is I can build a docker image just fine using the usual command: “docker build -t project/spring_backend .”

But it doesn’t work for Fly.io when I try to launch it:

 => ERROR [2/2] COPY target/*.jar app.jar                                                                          0.0s
------
 > [2/2] COPY target/*.jar app.jar:
------
Error: failed to fetch an image or build from source: error building: failed to solve: lstat /data/docker/tmp/buildkit-mount1012633289/target: no such file or directory

The dockerfile is the following:

FROM eclipse-temurin:21-jdk-alpine
VOLUME /tmp
COPY target/*.jar app.jar
ENTRYPOINT ["java","-jar","/app.jar"]

And the project structure is the following:

project
--src
--target
----generated.jar
--Dockerfile
--fly.toml

And the fly.toml just in case:

app = 'project'
primary_region = 'mad'

[build]

[http_service]
  internal_port = 8080
  force_https = true
  auto_stop_machines = true
  auto_start_machines = true
  min_machines_running = 0
  processes = ['app']

[[vm]]
  memory = '1gb'
  cpu_kind = 'shared'
  cpus = 1

I have been doing research and troubleshooting this for hours now and I don’t know what is happening, my first guess is that the build that fly.io creates somehow places my project somewhere else, and so /target isn’t where it should be, but I am at a loss.

I would appreciate any and all help, have a good day!

2

What that message means is one of two things is true:

  • target/*.jar is not present on your machine
  • target/*.jar is excluded by the contents of your .dockerignore file