Containers with volumes defined in Terraform report "host volumes are not supported"

[cmacrae]

Overview

I'm trying to define a container with a volume in Terraform for my on-prem install of SDC.
I understand the restrictions outlined here.
I've defined a container volume with 'container path' and 'volume name' properties, with the intention of using it to preserve data for another container (for use with 'volumes from') across upgrades/reprovisions.

However, despite passing no host volume parameters (this is just a container volume), the SDC Docker API returns a 500, stating 'host volumes are not supported'.

The Terraform declaration

resource "docker_container" "gogs_data" {
  image   = "${docker_image.alpine.latest}"
  name    = "gogs_data"
  volumes = {
    volume_name    = "data"
    container_path = "/data"    
  }
}

The error returned

Error applying plan:

1 error(s) occurred:

* docker_container.gogs_data: Unable to create container: API error (500): host volumes are not supported (fb24ffbf-db0f-4f92-9720-2c2f37876683)

Workarounds

I'm able to create such a container, with the same properties, using the standard docker command, though there is a strange responses during:

$ docker run -d -v /gogs_data --name gogs_data alpine:latest true 
bfb113a6341ae345c125b144fed755965cf72583a43245e1b368d81c9faafd9b
ERRO[0010] error getting events from daemon: Error response from daemon: (NotImplemented) events is not implemented (c0e6796b-23fd-4508-8f07-def38e3ca460)

$ docker run -it --volumes-from gogs_data --name gogs_test alpine:latest sh
ERRO[0010] error getting events from daemon: Error response from daemon: (NotImplemented) events is not implemented (1bcb5e00-e678-4f0a-8e4d-94061478dbba)
/ # ls -ld /gogs_data/
drwxr-xr-x    2 root     wheel            2 May  8 19:07 /gogs_data/

So, as you can see, it does indeed work. Just that for some reason, when defined via Terraform, the API seems to think I'm attempting to create a container with a host volume.

Please do let me know if there's any further debugging information I can provide, or any steps I can take to help out.

[askfongjojo]

Hi @cmacrae - It looks like Terraform translates the volume request to map a local volume to a host volume of the same name, i.e. turning it into something like:

docker run -d -v /gogs_data:/gogs_data --name gogs_data alpine:latest true 

To confirm this, you can check the docker log files to see if the request is passing host volume info (specifically the HostConfig.Binds property in the request payload).

[cmacrae]

Hey @askfongjojo - thanks for your response. Yeah, this was my inkling, too.
Thanks for the debugging tip, I'm away for a long weekend, but will take a look at the logs when I'm back and confirm.

If it is the case that Terraform is doing so, I'll raise the issue with them.

[cmacrae]

@askfongjojo Sorry for the late response.
I can confirm Terraform is changing the mapping to include a host configuration binding:

      "Volumes": {
        "/data": {}
      },
      "Entrypoint": null,
      "HostConfig": {
        "Binds": [
          "data:/data:rw"
        ],

I'll raise this with the Terraform guys - thanks for your help 👍