Support `netcat` in `grafana/agent` docker image

[eddumelendez]

Request

Testcontainers libraries check that the requested ports are open in the container executing the following piece of code. Currently, when trying to use the following definition

GenericContainer<?> grafanaAgent() {
    return new GenericContainer<>("grafana/agent:v0.37.2")
            .withExposedPorts(12345)
            .withCopyFileToContainer(
                    MountableFile.forClasspathResource("agent-config.river"),
                    "/etc/agent/agent-config.river"
            )
            .withEnv("AGENT_MODE", "flow")
            .withCommand("run", "--server.http.listen-addr=0.0.0.0:12345", "etc/agent/config.river");
}

the error below is displayed and the container doesn't start

check: Container.ExecResult(exitCode=137, stdout=, stderr=/bin/sh: 1: nc: not found
/bin/bash: connect: Cannot assign requested address
/bin/bash: line 1: /dev/tcp/localhost/12345: Cannot assign requested address
)

Use case

I'd like to use grafana/agent docker image with Testcontainers.

[thampiotr]

Seems like you should be able to use netcat by creating a new Docker image based on grafana/agent with netcat package installed. We want to keep our images lightweight and since Docker allows to easily extend them, it shouldn't prevent users from installing other programs when needed.

For the purpose of testing the containers, you may also want to consider checking for the open port from outside the container.

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