Ability to add new extrahost (new line into /etc/hosts file) to already created container

[igribkov]

Could somebody help me please?
I have already created container
In my create request testcontainers.ContainerRequest i've pass an extrahost, for example "some_host:192.168.1.11"
then i've call testcontainers.GenericContainer
and by some reasons before i will start this container i need to add one more extrahost
So the question is how to do this?

Same question about adding some extra env variables

[mdelapenya]

Hey @igribkov thanks for sending this question. It's possible to set the extrahost of a container leveraging the HostConfigModifier function in the ContainerRequest struct. Same for environment variables. I'm adding an example test that works:

func TestDockerContainerWithExtraHosts(t *testing.T) {
	ctx := context.Background()

	nginxC, err := GenericContainer(ctx, GenericContainerRequest{
		ProviderType: providerType,
		ContainerRequest: ContainerRequest{
			Image:        nginxAlpineImage,
			ExposedPorts: []string{nginxDefaultPort},
			Env:          map[string]string{"FOO": "BAR"},
			WaitingFor:   wait.ForListeningPort(nginxDefaultPort),
			HostConfigModifier: func(hc *container.HostConfig) {
				hc.ExtraHosts = []string{"DEV01:172.16.0.10", "DEV01:172.16.0.11"}
			},
		},
		Started: true,
	})

	require.NoError(t, err)
	terminateContainerOnEnd(t, ctx, nginxC)

	_, reader, err := nginxC.Exec(ctx, []string{"cat", "/etc/hosts"}, tcexec.Multiplexed())
	require.NoError(t, err)

	hostsBytes, err := io.ReadAll(reader)
	require.NoError(t, err)

	hosts := string(hostsBytes)

	assert.Contains(t, string(hosts), "172.16.0.10\tDEV01")
	assert.Contains(t, string(hosts), "172.16.0.11\tDEV01")
}

Please pay attention to the Env HostConfigModifier fields in the request struct 👀

[igribkov]

@mdelapenya tnx for reply

In your example you show how to add extrahost to container on creating request

could you please help to add extrahosts to container after it has been created
in your example let's add some code to add extrahosts after last assert.Contains

[mdelapenya]

@igribkov ah ok, I'm sorry, I thought your question was about container creation instead of "after it's been created and its running", right?

You can leverage the PostStarts container lifecycle hook, to inject a function that appends the entries you are interested. Please check the logs for the lifecycle hooks here, and an example here:

testcontainers-go/options_test.go

Lines 131 to 162 in 5562dbc

	func TestWithStartupCommand(t *testing.T) {
	req := testcontainers.GenericContainerRequest{
	ContainerRequest: testcontainers.ContainerRequest{
	Image: "alpine",
	Entrypoint: []string{"tail", "-f", "/dev/null"},
	},
	Started: true,
	}
	testExec := testExecutable{
	cmds: []string{"touch", "/tmp/.testcontainers"},
	}
	testcontainers.WithStartupCommand(testExec)(&req)
	assert.Equal(t, 1, len(req.LifecycleHooks))
	assert.Equal(t, 1, len(req.LifecycleHooks[0].PostStarts))
	c, err := testcontainers.GenericContainer(context.Background(), req)
	require.NoError(t, err)
	defer func() {
	err = c.Terminate(context.Background())
	require.NoError(t, err)
	}()
	_, reader, err := c.Exec(context.Background(), []string{"ls", "/tmp/.testcontainers"}, exec.Multiplexed())
	require.NoError(t, err)
	content, err := io.ReadAll(reader)
	require.NoError(t, err)
	assert.Equal(t, "/tmp/.testcontainers\n", string(content))
	}

.

The above snippet is creating a .testcontainers file in the /tmp dir leveraging the WithStartupCommand functional option. This option will execute the commands right after the container has started, but before your own test code, because it's coupled with the container lifecycle.

If you want to add an entry after some assertions, which could purely represent a different test case, you could directly call the container.Exec method to modify the file with the same commands you could have used in the above alternative. A valid solution for this could be reading the file from outside the container, modifying the bytes in the tests, and copying them back to the container.

[igribkov]

@mdelapenya, tnx a lot for your response.
testcontainers.WithStartupCommand() that's exactly what i need

[mdelapenya]

At the end of the day, the WithStartupCommand calls the container.Exec method 😉

[mdelapenya]

I'm closing this discussion as resolved, thanks for asking!