Programmatically check if Docker container process ended with non-zero status - docker

Question

I'm working on a Go application which starts some Docker containers using Go Docker SDK. I need to check if containers' processes exit with zero (success) status code.
Here's the minimal working example:
package main
import (
"context"
"io"
"log"
"os"
"github.com/docker/docker/api/types"
"github.com/docker/docker/api/types/container"
"github.com/docker/docker/client"
)
func main() {
ctx := context.Background()
cli, err := client.NewEnvClient()
if err != nil {
log.Fatal(err)
}
reader, err := cli.ImagePull(
ctx,
"docker.io/library/alpine",
types.ImagePullOptions{},
)
if err != nil {
log.Fatal(err)
}
io.Copy(os.Stdout, reader)
resp, err := cli.ContainerCreate(ctx, &container.Config{
Image: "alpine",
Cmd: []string{"sh", "-c", "echo hello world; return 1"},
Tty: true,
}, nil, nil, "")
if err != nil {
log.Fatal(err)
}
err = cli.ContainerStart(
ctx,
resp.ID,
types.ContainerStartOptions{},
)
if err != nil {
log.Fatal(err)
}
statusCh, errCh := cli.ContainerWait(
ctx,
resp.ID,
container.WaitConditionNotRunning,
)
select {
case err := <-errCh:
if err != nil {
log.Fatal(err)
}
case <-statusCh:
}
out, err := cli.ContainerLogs(
ctx,
resp.ID,
types.ContainerLogsOptions{ShowStdout: true},
)
if err != nil {
log.Fatal(err)
}
io.Copy(os.Stdout, out)
}
As you can see, the process in the container ends with non-zero status (sh -c "echo hello world; return 1"). However, it doesn't log any fatal errors and simply displays hello world when built and executed:
{"status":"Pulling from library/alpine","id":"latest"}
{"status":"Digest: sha256:7043076348bf5040220df6ad703798fd8593a0918d06d3ce30c6c93be117e430"}
{"status":"Status: Image is up to date for alpine:latest"}
hello world
How can I check that container process exited with non-zero status using Docker Go SDK?

Answer 1

I think you should use the status channel to get the exit code. The error channel seems to be used to signal if there was an error while talking to the docker daemon, see https://godoc.org/github.com/docker/docker/client#Client.ContainerWait.
This works for me:
select {
case err := <-errCh:
if err != nil {
log.Fatal(err)
}
case status := <-statusCh:
log.Printf("status.StatusCode: %#+v\n", status.StatusCode)
}