Invalid environment variables, rkt volume with dash or underscore in task name

[blalor]

• Nomad v0.5.4
• CentOS Linux release 7.3.1611 (Core), 4.9.10-1.el7.elrepo.x86_64
• rkt Version: 1.24.0

job "example" {
    group "example" {
        task "$TASK0" {
            driver = "rkt"

            config {
                image = "example.com/aci0:LATEST"

                port_map {
                    api = "api"
                }
            }
        }
        
        task "othertask" {
            driver = "rkt"
            
            config {
                image = "example.com/aci1:LATEST"
            }
    }
}

1. If $TASK0 is set to log-ingester, rkt run will fail for the second (othertask) task because Nomad attempts to set the environment variable NOMAD_ADDR_log-ingester_api, and the - is not a valid environment variable name, per the ACI spec (IEEE Std 1003.1-2001).

2. If $TASK0 is set to log_ingester (trying to work around the above problem), rkt run will fail for the first (log_ingester/$TASK0) task because Nomad creates invalid volume names for the local, alloc, and secret directories:

    Error: invalid argument "$ALLOC_ID-log_ingester-alloc,kind=host,source=…" for --volume=$ALLOC_ID-log_ingester-alloc,kind=host,source=…:
        invalid value in --volume flag "$ALLOC_ID-log_ingester-alloc,kind=host,source=…":
            ACName must contain only lower case alphanumeric characters plus "-"
   

ACName must be ^[a-z0-9]+([-][a-z0-9]+)*$

The workaround for both of these is to make the task name match ^[a-z0-9]+$. The 2nd issue is obviously rkt-specific, but unless the Docker driver does something different about the environment variables, they're of limited use with bash, for example.

[blalor]

related to #2406 #2405

[schmichael]

1. is fixed by Replace "-" in port labels with "_" for env vars #2406 (there's an attached binary you can test with if you have time); working on 2. now.

My plan is to just escape underscores with dashes in rkt volume names since we just need a task unique name.

A safer approach would be to hash+base32 task names in volumes as the volume name just needs to be unique, but I'd really like to make the names human readable if possible.

[schmichael]

#2416 should enforce env var name compliance with the standard.

[github-actions]

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