[Bug 1875882] Re: debconf attempts interactive configuration; breaks Docker image builds

[Tianon Gravi]

** Also affects: debconf (Ubuntu)
   Importance: Undecided
       Status: New

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https://bugs.launchpad.net/bugs/1875882

Title:
  debconf attempts interactive configuration; breaks Docker image builds

Status in cloud-images:
  New
Status in debconf package in Ubuntu:
  New

Bug description:
  When I build a container image using a Dockerfile based on the
  official "ubuntu" image, if I try to install packages that use debconf
  to obtain configuration information, the build fails because debconf
  tries to interact with the user (which is not possible when building a
  container, since the build process must be non-interactive).

  How to reproduce:

  1) install Docker (the version doesn't seem to matter; tried with
  various 19.03 variants)

  2) run the following command to try and build an image:

  ```
  docker build - <<EOF
  FROM ubuntu
  RUN apt-get update
  RUN apt-get install -y perl-modules tzdata
  EOF
  ```

  The build remains stuck when debconf ask the "Geographic area:".

  Notes:

  A) The problem doesn't appear when trying to install tzdata by itself
  (without perl-modules), because then debconf hits a bug and bails out
  with a zero status code, allowing the package install to succeed:

  ```
  Use of uninitialized value $_[1] in join or string at /usr/share/perl5/Debconf/DbDriver/Stack.pm line 111.
  ```

  B) If you wonder "why is this person trying to install tzdata in a
  container?!?" - I'm not! But tzdata is a dependency of many other
  packages. When trying to reproduce the bug, I reduced it to the
  simplest case I could find (which was tzdata + perl-modules).

  C) That problem did not happen in 16.04 (you can check by replacing
  "FROM ubuntu" with "FROM ubuntu:16:04" in the repro above). It did
  happen in 18.04, but it was less likely to show up, because tzdata was
  less depended upon. I have Dockerfiles that worked with 18.04, and
  break with 20.04, because they install packages that didn't depend on
  tzdata in 18.04, but do depend on tzdata in 20.04.

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