How to fix Github Docker Containers Built with Actions

Following on from having set up the Github Container Registry in my previous post I look at how I can combine Github Actions with the Registry to automate the build step of my application.

tl;dr

You can use Github Actions to build containers based on Dockerfiles in your repository.
Have a Google for the answer but don't hesitate to run your problematic containers interactively.
You can build and interact with your Docker images locally docker build . then docker run -it $IMAGE_ID /bin/bash

Problem

I have a Dockerfile I am building to package up my application to be deployed somewhere, I do so using a Github Action upon pushing changes
to Github.

Github Actions have many example templates to base workflows on if you already have a project you can navigate to: "https://github.com/" + $YOUR_USERNAME + "/" + $REPOSITORY_NAME + "/actions/new

When I create a Dockerfile, I develop locally and commit changes to the repository. Upon a push to Github my Action Workflow is triggered, this is continuous integration (CI) at it's best, but when we need to look inside a container things can get a little tricky.

What follows are some notes about how you might fix your CI container build.

Lessons learnt

When I attempt to build this Dockerfile, which looks like this:

FROM rustlang/rust:nightly-slim AS build
WORKDIR /src/rust-web-template
COPY . .
RUN cd ./collector && cargo build --release && cd ..
FROM ubuntu:18.04
COPY --from=build /src/rust-web-template/target/release/collector /usr/local/bin/collector
CMD ["usr/local/bin/client"]

Here are some issues I ran into:

pkg-config is required for locating dependencies such as SSL within the container's linux.

It looks like you're compiling on Linux and also targeting Linux. Currently this
requires the `pkg-config` utility to find OpenSSL but unfortunately `pkg-config`
could not be found. If you have OpenSSL installed you can likely fix this by
installing `pkg-config`.

Docker container builds steps that require approval must have a yes flag passed to them apt-get install -y pkg-config.

Do you want to continue? [Y/n] Abort.
The command '/bin/sh -c apt-get update &&     apt-get install pkg-config' returned a non-zero code: 1

We need to run apt-get update to ensure our container knows where to get packages we want to install.

E: Package 'pkg-config' has no installation candidate

Dependencies such as Openssl need to be installed as well to be available when compiling an application that depends on it.

run pkg_config fail: "`\"pkg-config\" \"--libs\" \"--cflags\" \"openssl\"` did not exit successfully: exit code: 1\n--- stderr\nPackage openssl was not found in the pkg-config search path.\nPerhaps you should add the directory containing `openssl.pc\'\nto the PKG_CONFIG_PATH environment variable\nNo package \'openssl\' found\n"

How can we debug a Docker container without Googling?

So our Dockerfile now looks like this:

FROM rustlang/rust:nightly-slim AS build
WORKDIR /src/rust-web-template
COPY . ./collector
RUN apt-get update -y && \
    apt-get install -y pkg-config \
    libssl-dev
RUN cd ./collector && cargo build --release && cd ..
FROM ubuntu:18.04
COPY --from=build /src/rust-web-template/target/release/collector /usr/local/bin/collector
CMD ["usr/local/bin/client"]

I received the following error, which tells me that a directory path was not correct.

 COPY failed: stat /var/lib/docker/overlay2/640cf4644f3f681a1b78f9507d80e70f3cae1a189a65dfd6a1f26f7313748161/merged/src/rust-web-template/target/release/collector: no such file or directory

To fix this I comment out the code, as we need to build the container and then interact with it.

FROM rustlang/rust:nightly-slim AS build
WORKDIR /src/rust-web-template
COPY . ./collector
RUN apt-get update -y && \
    apt-get install -y pkg-config \
    libssl-dev
RUN cd ./collector && cargo build --release && cd ..
+ #FROM ubuntu:18.04
+ #COPY --from=build /src/rust-web-template/target/release/collector /usr/local/bin/collector
+ #CMD ["usr/local/bin/client"]

Next we build it by running $ docker build -t debugimage ., and then we can run the container interactively to explore it docker run -it --name debugimage:latest /bin/bash

Once inside we can run our bash commands to investigate.

t@d0e323387e63:/src/rust-web-template# ls
collector
root@d0e323387e63:/src/rust-web-template# cd collector/
root@d0e323387e63:/src/rust-web-template/collector# ls
Cargo.lock  Cargo.toml  Dockerfile  src  target
root@d0e323387e63:/src/rust-web-template/collector# cd tar
bash: cd: tar: No such file or directory
root@d0e323387e63:/src/rust-web-template/collector# cd target
root@d0e323387e63:/src/rust-web-template/collector/target# ls
CACHEDIR.TAG  release
root@d0e323387e63:/src/rust-web-template/collector/target# cd release/
root@d0e323387e63:/src/rust-web-template/collector/target/release# pwd
/src/rust-web-template/collector/target/release
root@d0e323387e63:/src/rust-web-template/collector/target/release# ls
build  collector  collector.d  deps  examples  incremental
root@d0e323387e63:/src/rust-web-template/collector/target/release# pwd
/src/rust-web-template/collector/target/release
root@d0e323387e63:/src/rust-web-template/collector/target/release#

Then update the path in the Docker container, and uncomment out lines that were not working.

- COPY --from=build /src/rust-web-template/target/release/collector /usr/local/bin/collector
+ COPY --from=build /src/rust-web-template/collector/target/release/collector /usr/local/bin/collector

And then we can $ exit our interactive container session.

Upon building the image again the path problem shouldn't cause the build to fail!

The working code for this can be found here.