19.03.0-beta1: docker context commands hang if current engine is not reachable

[StefanScherer]

Description

After switching to an unreachable Docker context, all the docker context commands hang. It seems like the docker CLI talks too early with the remote engine.

Steps to reproduce the issue:

1. Create a docker context remote for a remote Docker engine, or simulate it with
   docker context create remote --docker "host=tcp://1.2.3.4:2375"
2. docker context use remote
3. Turn off WiFi/network connection, not needed if you simulate it
4. Run docker context ls
5. Run docker context use default
6. Run docker context -h

Describe the results you received:

Commands in step 4. - 6. will hang for a long time and gives a bad user experience.

Describe the results you expected:

The commands docker context ls and docker context use should work without communicating with the Docker engine of the current context.
Reason: To easily switch back to Docker Desktop without a delay.

Additional information you deem important (e.g. issue happens only occasionally):

Output of docker version:

$ docker version
Client: Docker Engine - Community
 Version:           19.03.0-beta1
 API version:       1.39 (downgraded from 1.40)
 Go version:        go1.12.1
 Git commit:        62240a9
 Built:             Thu Apr  4 19:15:32 2019
 OS/Arch:           darwin/amd64
 Experimental:      false

Output of docker info:

(paste your output here)

Additional environment details (AWS, VirtualBox, physical, etc.):

Interesting detail when I use the default context (Docker Desktop in my case) a docker context use remote is also fast, so switching to a context that is not reachable works as expected.

[silvin-lubecki]

Hello @StefanScherer , thanks for your contribution, but I will close this issue as I think this is a duplicate of #1739.
By the way there is a PR trying to fix it #1747 , but on hold for the moment. Thanks 👍

[silvin-lubecki]

Feel free to re-open it if you think it's not a duplicate 👍

[JAForbes]

For anyone else landing on this, you can work around the CLI hanging by setting the DOCKER_CONTEXT environment variable.

# hangs because pointing to a non existent remote context
$ docker context ls

# force docker to ignore the old context without using CLI
$ export DOCKER_CONTEXT=default

# No longer hangs
$ docker context ls
NAME        DESCRIPTION                               DOCKER ENDPOINT               KUBERNETES ENDPOINT   ORCHESTRATOR
default *   Current DOCKER_HOST based configuration   unix:///var/run/docker.sock                         swarm
remote                                                ssh://root@XXX.XXX.XXX.XXX

$ docker context rm remote
remote