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I'm looking at wurstmeister/kafka-docker, and found this pull suggesting using the IP address. Basically, it uses the docker info formatting: 

HOSTNAME_COMMAND: "docker info -f '{{`{{.Swarm.NodeAddr}}`}}'"

I get the idea that it uses the formatting to get the address, but I don't understand what's going on with the extra {{...}} and the backticks (which would normally be an eval). docker-compose allows for ${variables}, but there's no dollar sign ($) here, so no need to escape. Why isn't this just: 

HOSTNAME_COMMAND: "docker info -f '{{.Swarm.NodeAddr}}'"

I've seen this elsewhere, so I assume there's a reason.

OneCricketeer
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mconner
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1 Answers1

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This is basically a duplicate of this post. However, you might not find that one if you aren't aware that docker-compose files use Go templates (I didn't find any mention of it in the compose file reference). So basically, in go, the backquotes indicate a literal string, so the outer set of {{ }} is a template allowing for the backquotes to take everything between literally.

mconner
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