Provide better error messages for cmds requiring the docker daemon in Cloud Shell

[jluk]

Due to the fact the docker daemon cannot run in Cloud Shell since shell itself is a container, certain az cmds do not work properly.

I propose we work together to output more useful error messages for all the cases this is true for az. @yugangw-msft

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Environment summary

Azure Cloud Shell (Bash)

gordon@Azure:~$ az acr login --name http://sapetregistry.azurecr.io 
Please verify if docker daemon is running properly.

[derekbekoe]

Doesn't this specifically apply to ACR commands?

[yugangw-msft]

Doesn't this specifically apply to ACR commands?

That is correct

[jluk]

It does apply to ACR but I think it may apply to other cmds in AKS/ACS if they are docker dependent

[djyou]

This message isn't technically wrong but is there a flag that can indicate the CLI is running in cloud shell?

We could show this command is not supported in cloud shell but for general cases running CLI in a container, there is workaround to enable acr login.

/cc @sajayantony

[yugangw-msft]

is there a flag that can indicate the CLI is running in cloud shell?

Yes, there is a util that checks an agreed on env var

[djyou]

@jluk @sajayantony Can we agree on what the message would be in cloud shell? This may also apply to other docker dependent commands if any.

This command is not supported in Azure Cloud Shell.

[yugangw-msft]

2 cents, can we briefly mention the reason in the message that because the docker is not available in cloud shell?

[jluk]

What do we think about the following?

This command requires running the docker daemon, which is not supported in Azure Cloud Shell. Try using [docker-machine](https://docs.docker.com/machine/overview/) which is already installed in Cloud Shell.

[yugangw-msft]

Have not used docker machine, but wording wise it looks good to me.

[djyou]

Agreed on the wording. The link for docker-machine didn't provide enough info on how to create a docker machine (a new vm) in Azure and run docker daemon in it. IMO, It might invite more usability questions.

[jluk]

Fair point - what do you think about this doc? https://docs.docker.com/machine/get-started/#create-a-machine

The Azure specific driver doc is here: https://docs.docker.com/machine/drivers/azure/

[jluk]

Including @yolo3301 in case he has input for a good error message routing users to use docker-machine instead