gcloud command for bulk metadata update

Question

I am trying to craft a gcloud command that does a bulk metadata update on compute engine instances.

Normally I could just pipe gcloud compute instances list to xargs gcloud compute instances add-metadata. However, this is thwarted because for some inexplicable reason, add-metadata needs both an instance name, and a zone, even though compute instance names appear to be globally unique. So now I'm forced to try to shuttle both pieces of data (both name and zone) to the add-metadata command. If I don't provide both, I get:

ERROR: (gcloud.compute.instances.add-metadata) Underspecified resource [worker-1]. Specify the [--zone] flag.

I'm about ready to give up on the bash/xargs incantation and switch to python but I thought I'd check here first.

I have this command:

gcloud compute instances list \
        --filter="name~'worker' AND zone~'us-central1'" \
        --format 'value(name,zone)'

which returns something like:

worker-1    us-central1-c
worker-2    us-central1-c
worker-3    us-central1-c
worker-4    us-central1-c

I then need to pipe these into a command like:

gcloud compute instances add-metadata --zone=[zone goes here] --metadata myvalue=true [instance name goes here]

But this is proving tricky/annoying using xargs alone. Is there a better or simpler way to accomplish what I'm attempting?

Answer 1

Pipe it to while read sequence:

gcloud compute instances list \
       --filter="name~'worker' AND zone~'us-central1'" \
       --format 'value(name,zone)' | \
while read instance zone; do
    gcloud compute instances add-metadata \
    --zone=$zone --metadata myvalue=true $instance
done