Document how to get socket location for image building configuration with podman

[andrej-urvantsev]

At the moment current documentation recommends this approach to configure PodMan:

tasks.named<BootBuildImage>("bootBuildImage") {
	docker {
		host.set("unix:///run/user/1000/podman/podman.sock")
		bindHostToBuilder.set(true)
	}
}

Where 1000 is an uid of a user, which is usually a 1000, but might be different in some cases.

So, more generic approach to configure PodMan(in theory it's also compatible with Docker) would be:

tasks.named<BootBuildImage>("bootBuildImage") {
    docker {
        fun String.runCommand(
            workingDir: File = File("."),
            timeoutAmount: Long = 60,
            timeoutUnit: TimeUnit = TimeUnit.SECONDS
        ): String? = runCatching {
            ProcessBuilder("\\s".toRegex().split(this))
                .directory(workingDir)
                .redirectOutput(ProcessBuilder.Redirect.PIPE)
                .redirectError(ProcessBuilder.Redirect.PIPE)
                .start().also { it.waitFor(timeoutAmount, timeoutUnit) }
                .inputStream.bufferedReader().readText().trim()
        }.onFailure { it.printStackTrace() }.getOrNull()

        val uid = "id -u".runCommand() ?: 0;
        val socketPath = "/run/user/$uid/podman/podman.sock";
        if (file(socketPath).exists()) {
            host.set("unix://$socketPath")
            bindHostToBuilder.set(true)
        }
    }
}

Which is ugly. It would be nice to move this logic inside of Spring Boot Gradle(and probably maven) plugins to eliminate that boilerplate from configs.

[mhalbritter]

On my system, an env variable UID is populated, which can be used with Gradle. Would that be an acceptable workaround?

[andrej-urvantsev]

There is something special about that variable:

# In terminal
echo ${UID}                            
1000

but System.getenv("UID") in java returns null.

I mean that it's possible to come up with some workarounds, but it would be much better if Spring Boot plugin could auto-detect PodMan.

[mhalbritter]

Huh, you're right. It's not shown in env output, either. TIL.

[andrej-urvantsev]

I think it's set in shell(in bash or zsh for example) - not globally.

[scottfrederick]

With podman installed, you can run the command podman info -f "{{.Host.RemoteSocket.Path}}") to get the socket that should be used to connect to it. With this, you can set the DOCKER_HOST environment variable that many tools will use to connect (for example, on Linux export DOCKER_HOST="unix://$(podman info -f "{{.Host.RemoteSocket.Path}}")").

That's enough for Spring Boot to use podman for downloading the builder and run images, as well as any configured buildpack images, since the Boot plugins will honor the DOCKER_HOST environment variable. The other part is that the processes running inside the builder image need to connect to the podman socket, which is what the docker.bindHostToBuilder option does. If you can set the DOCKER_HOST environment variable, then this would be as simple as checking for that in your build script and setting bindHostToBuilder accordingly (as this user is doing).

@lazystone Does this technique suit your needs?

[andrej-urvantsev]

Ok, that's way better than mine approach. But what would be a downside to do following by default inside the plugin?

val dockerHost = System.getenv("DOCKER_HOST")
if (dockerHost != null) {
    docker {
        host.set(dockerHost)
        bindHostToBuilder.set(true)
    }
}

I guess if DOCKER_HOST environment variable is defined, then it should be used by all sub-processes anyway?

[scottfrederick]

I guess if DOCKER_HOST environment variable is defined, then it should be used by all sub-processes anyway?

That's not necessarily true. In the minikube example, it is necessary to set the address of the Docker host as a remote address (not a socket), but bindHostToBuilder is not required because minikube exposes the default /var/run/docker.sock socket location inside of running containers. This is dependent on how each Docker-like daemon chooses to implement things.

I think it would be good to add a note about the podman info command to the Boot documentation to make it more clear how you should get the value to provide to docker.host, but I'm not sure we can assume anything more than we currently do.