[SOLVED] Docker - Alpine Elixir container has unsatisfiable constraints

Docker - Alpine Elixir container has unsatisfiable constraints

I have this Dockerfile for my Phoenix application. When running a promotion with Semaphore CI, my deployment fails and returns this error:

ERROR: unsatisfiable constraints:
  libssl1.0 (missing):
    required by: world[libssl1.0]
  pdftk (missing):
    required by: world[pdftk]

How come it can't fetch these two packages?

Solution

The erlang:20-alpine image (Dockerfile), which is used as base for elixir:1.6.6-alpine (Dockerfile), has been recently updated from Alpine 3.8 to 3.9 (Github commit).

The following has changed between Alpine 3.8 and 3.9:

The libssl1.0 package has been removed, and superseded by libssl1.1.
The pdftk package has been removed in 3.9, and is only available in the edge branch community repository (and older Alpine branches).

libssl:

This one is easily fixed: just replace the libssl1.0 package with libssl1.1.

pdftk:

pdftk is more problematic. It depends on libgcj6, the Java runtime for GCC 6. However, the Java runtime was completely removed from GCC 8 and onwards. libgcj6 is the Java runtime for GCC 6, and is not compatible with GCC 8. Installing libgcj6 also pulls the GCC 6 C++ runtime, libstdc++6 (6.4.0-r9).

An attempt to install pdftk along with libgcj6, for example:

RUN apk add --no-cache libgcj6 pdftk --repository=http://dl-cdn.alpinelinux.org/alpine/edge/community

Fails with:

ERROR: unsatisfiable constraints:
  so:libgcj.so.17 (missing):
    required by: pdftk-2.02-r1[so:libgcj.so.17]

Unfortunately, I'm not familiar with a workaround, currently.

There's an active open Alpine ticket for this issue: https://bugs.alpinelinux.org/issues/10136, so it's worth keeping an eye for possible updates.