Docker swarm service environment variable is not visible within container - docker

Question

I am creating a docker service with an environment variable:
docker service create --env TEST=123 myservice
And I verify the environment variable was set with
$ docker service inspect myservice
...
ContainerSpec:
Env: TEST=123
...
But then the environment variable does not show up within the docker container. In particular, the code running inside the docker container prints os.Environ() and in the logs I see only the standard environment variable:
$ docker service logs myservice
[HOSTNAME=48bcddab9204 SHLVL=1 HOME=/root PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin PWD=/app]
So the environment variable "TEST" is not set. How can I set up a service that defines this environment variable?
The output of docker version is
Client:
Version: 20.10.12
API version: 1.41
Go version: go1.17.5
Git commit: e91ed5707e
Built: Mon Dec 13 22:31:40 2021
OS/Arch: linux/amd64
Context: synology
Experimental: true
Server:
Engine:
Version: 20.10.3
API version: 1.41 (minimum version 1.12)
Go version: go1.15.13
Git commit: a3bc36f
Built: Thu Aug 19 07:11:25 2021
OS/Arch: linux/amd64
Experimental: false
containerd:
Version: v1.4.3
GitCommit: ea3508454ff2268c32720eb4d2fc9816d6f75f88
runc:
Version: v1.0.0-rc93
GitCommit: 31cc25f16f5eba4d0f53e35374532873744f4b31
docker-init:
Version: 0.19.0
GitCommit: ed96d00

Answer 1

Variables should be defined in the environment when you use --env. If that's not happening, we'd need a complete example to reproduce. Here's an example showing that it works:
$ docker service create --name env-test --env TESTVAR=123 busybox tail -f /dev/null
nj9l6z57d9pviztyp9pglmv4r
overall progress: 1 out of 1 tasks
1/1: running [==================================================>]
verify: Service converged
$ docker ps -l
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
697c1bf221b1 busybox:latest "tail -f /dev/null" 20 seconds ago Up 19 seconds env-test.1.vlrepc8mqqvx7gysh2qsymja8
$ docker exec -it env-test.1.vlrepc8mqqvx7gysh2qsymja8 env
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
HOSTNAME=697c1bf221b1
TERM=xterm
TESTVAR=123
HOME=/root