CODEWITHSUNDEEP
dockeramazon-ec2docker-composedocker-swarm
jaks
jaks

Reputation: 4607

Hostname in docker compose file v3 is not accepted

I am trying to set the hostname for the container as hostname: '{{.Node.Hostname}}' in docker compose v3 in AWS EC2.

It is failing as Error response from daemon: rpc error: code = 3 desc = expanding hostname failed: template: expansion:1:7: executing "expansion" at <.Node.Hostname>: can't evaluate field Hostname in type struct { ID string }.

Here are the version details,

Client:
 Version:      17.06.2-ce
 API version:  1.30
 Go version:   go1.8.4
 Git commit:   3dfb8343b139d6342acfd9975d7f1068b5b1c3d3
 Built:        Fri Nov 10 00:50:37 2017
 OS/Arch:      linux/amd64

Server:
 Version:      17.06.2-ce
 API version:  1.30 (minimum version 1.12)
 Go version:   go1.8.4
 Git commit:   402dd4a/17.06.2-ce
 Built:        Fri Nov 10 00:51:08 2017
 OS/Arch:      linux/amd64
 Experimental: false

As per https://docs.docker.com/compose/compose-file/, 17.06.+ is compatible with docker-compose v3.

How I can make this templating work? Do I need to upgrade the docker? Thanks.

Upvotes: 0

Views: 1900

Answers (1)

Bret Fisher
Bret Fisher

Reputation: 8616

This now works with compose files and v17.12 (Dec 2017 stable release) of Docker, but only works when used with Swarm Stacks.

I think you're using Swarm so just update your docker version and you should be good, but here's more info for others in case they are just trying single node docker-compose up, which won't work with templates.

docker-compose does not interpret go templates like Swarm does.

In addition, the .Node.Hostname is a Swarm-specific label, so you can't use it with docker-compose up on a single server, which doesn't have access to that label.

Just to verify, when I use this compose file:

version: "3.4"

services:
  nginx:
    image: nginx
    hostname: '{{.Node.Hostname}}'

In docker-compose this is what I got:

docker-compose up -d
docker-compose exec nginx hostname
{{.Node.Hostname}}

Then if I use that file in Swarm Stacks:

docker stack deploy -c docker-compose.yml hn
# find the node and container ID of that service task
# found them on node 1 with hostname "swarm1"
docker exec 0a087 hostname
swarm1

If you need to use docker-compose in a single node and get the hostname into the compose file, maybe use variable substitution, then set the hostname to a variable and then docker-compose up will replace the variable in the compose file.

Upvotes: 1

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