Build context parameter in docker-compose can not be parsed as string

[mre]

Given the following Dockerfile:

FROM debian:jessie

and this docker-compose.yml

services:
  app:
    build: .

I get an error when I run crane up:

ERROR: yaml: unmarshal errors:
  line 3: cannot unmarshal !!str `.` into crane.BuildParameters

The above syntax is valid, according to the official version 2 docker-compose reference.

If I change the docker-compose.yml to look like this, it works:

services:
  app:
    build:
      context: .

[michaelsauter]

Thanks for the detailed report.

Crane aims to be docker-compose v3 compatible. However, in this case both v2 and v3 are the same, and they do support a string for build, not just an object.

I propose the following:

1. I'll add the incompatibility to the list of differences between Crane and Docker Compose
2. Then we can look into allowing a string for build as well.

Do you want to have a look into fixing it? If not, I will have a look at it sometime this month, but it is not top priority as there is a work-around.

[mre]

No worries, it's a minor thing. Just wanted to document the behaviour somewhere in case anybody else hits the same issue. 😉