Building a CentOS 7.x Docker image

[moensch]

Creates a buildkite/agent docker image based on centos:7.7.1908.

Sadly, image size came out to be 757MB, compared to 466MB for the current 3.16.0-ubuntu image. Suggestions for further size reduction welcome.

A couple of notes:

• openssh-client is openssh-clients on CentOS
• crontabs package is what provides /bin/run-parts used in the entrypoint
• CentOS does not provide jq, but EPEL does
• Both CentOS and EPEL have rather old docker versions, installing from docker-ce directly

[keithpitt]

This looks good to me. I'll wait for a double check from @buildkite/golang first.

[pda]

Seems good;

I can reproduce the docker build locally:

go build -o packaging/docker/centos-linux/buildkite-agent
docker build --tag tmp packaging/docker/centos-linux

Here's a diff against the ubuntu Dockerfile; changes look legit to me;

for f in packaging/docker/centos-linux/*; do diff -u "$f" "${f/centos/ubuntu}"; done

--- packaging/docker/centos-linux/Dockerfile	2019-12-11 11:58:28.035835826 +1100
+++ packaging/docker/ubuntu-linux/Dockerfile	2019-11-15 12:22:44.795548141 +1100
@@ -1,20 +1,19 @@
-FROM centos:7.7.1908
+FROM ubuntu:18.04
 
-RUN yum -y install \
+ENV DEBIAN_FRONTEND=noninteractive
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
       curl \
       ca-certificates \
       bash \
       git \
       perl \
       rsync \
-      openssh-clients \
+      openssh-client \
       curl \
-      crontabs \
-      epel-release \
-    && yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo \
-    && yum -y install docker-ce jq \
-    && yum clean all \
-    && rm -rf /var/cache/yum*
+      docker.io \
+      jq \
+    && rm -rf /var/lib/apt/lists/*
 
 RUN curl -Lfs -o /sbin/tini  https://github.com/krallin/tini/releases/download/v0.18.0/tini \
     && chmod +x /sbin/tini \

I've (rip)grepped to verify centos is being handled in this branch everywhere that ubuntu is mentioned in master in the .buildkite/ and packaging/docker/ dirs that this PR touches.

🚢