`docker context use` shared between terminal sessions

[enisdenjo]

Description

Setting a Docker context with docker context use shares the used context between terminal sessions. This is quite dangerous IMHO and almost made me to mess up a production environment since the old behaviour attached the context exclusively to the current session.

I guess this was rolled out with a new version, sure; but, since I am now paranoid and repulsive with using contexts, is there any possibility to disable this behaviour (have a context stick to the current terminal session like it was before)?

Steps to reproduce the issue:

1. docker context use chocolate
2. Open new terminal (window, tab or even a new terminal app like iTerm2 vs Terminal.app)
3. docker context show prints chocolate

Describe the results you received:

Opening a new terminal and doing docker context show prints chocolate.

Describe the results you expected:

Opening a new terminal and doing docker context show prints default.

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

Happens consistently. And quite dangerous IMHO, simply because you might have forgotten you set a production environment context and did a docker compose down -v.

Output of docker version:

Client: Docker Engine - Community
 Cloud integration: 1.0.12
 Version:           20.10.5
 API version:       1.41
 Go version:        go1.13.15
 Git commit:        55c4c88
 Built:             Tue Mar  2 20:13:00 2021
 OS/Arch:           darwin/amd64
 Context:           default
 Experimental:      true

Server: Docker Engine - Community
 Engine:
  Version:          20.10.5
  API version:      1.41 (minimum version 1.12)
  Go version:       go1.13.15
  Git commit:       363e9a8
  Built:            Tue Mar  2 20:15:47 2021
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          1.4.4
  GitCommit:        05f951a3781f4f2c1911b05e61c160e9c30eaa8e
 runc:
  Version:          1.0.0-rc93
  GitCommit:        12644e614e25b05da6fd08a38ffa0cfe1903fdec
 docker-init:
  Version:          0.19.0
  GitCommit:        de40ad0

Output of docker info:

Client:
 Context:    default
 Debug Mode: false
 Plugins:
  app: Docker App (Docker Inc., v0.9.1-beta3)
  buildx: Build with BuildKit (Docker Inc., v0.5.1-docker)
  scan: Docker Scan (Docker Inc., v0.6.0)

Server:
 Containers: 9
  Running: 2
  Paused: 0
  Stopped: 7
 Images: 67
 Server Version: 20.10.5
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Native Overlay Diff: true
 Logging Driver: json-file
 Cgroup Driver: cgroupfs
 Cgroup Version: 1
 Plugins:
  Volume: local
  Network: bridge host ipvlan macvlan null overlay
  Log: awslogs fluentd gcplogs gelf journald json-file local logentries splunk syslog
 Swarm: inactive
 Runtimes: io.containerd.runtime.v1.linux runc io.containerd.runc.v2
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: 05f951a3781f4f2c1911b05e61c160e9c30eaa8e
 runc version: 12644e614e25b05da6fd08a38ffa0cfe1903fdec
 init version: de40ad0
 Security Options:
  seccomp
   Profile: default
 Kernel Version: 5.10.25-linuxkit
 Operating System: Docker Desktop
 OSType: linux
 Architecture: x86_64
 CPUs: 8
 Total Memory: 1.94GiB
 Name: docker-desktop
 ID: OFMV:OP7D:3KQH:Z7SF:4XNY:DXTV:XW5P:NG6T:Y7ZN:XFWX:YAZN:QV6J
 Docker Root Dir: /var/lib/docker
 Debug Mode: false
 HTTP Proxy: http.docker.internal:3128
 HTTPS Proxy: http.docker.internal:3128
 Registry: https://index.docker.io/v1/
 Labels:
 Experimental: false
 Insecure Registries:
  127.0.0.0/8
 Live Restore Enabled: false

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

Just my Mac.

[thaJeztah]

This is the expected behaviour for docker context use, as it configures the default context for the CLI to use. To switch context in a specific shell, or for a single command, you can use the DOCKER_CONTEXT environment variable instead.

That said, I think it makes sense to more explicitly mention this (and to show the alternative uses).

[enisdenjo]

Awesome! Doing export DOCKER_CONTEXT=chocolate makes sense. Thanks!

[thaJeztah]

Note that with docker 20.10, we added the active context to the output of docker version, which could be used to (e.g.) include it in your prompt; see https://github.com/docker/cli/pull/2500 (note that docker version will still make a connection with the daemon, so it may still not be ideal, but perhaps it's useful for your scenario)

[thaJeztah]

Docs now mention the docker context show command; https://docs.docker.com/reference/cli/docker/context/show/

We probably should still tweak the documentation for docker context use to;

• Describe that it's updating the CLI's configuration file (so change is "sticky")
• Describe that this affects all terminals (due to it being a configuration change)
• Show some examples with DOCKER_CONTEXT=xxx and --context to illustrate those can be used to temporarily switch, or to change the context for a specific shell (export DOCKER_CONTEXT=xxx ...)