Fix tini and docker-compose for ubuntu-20.04

packaging/docker/ubuntu-20.04-linux/Dockerfile

@@ -1,35 +1,36 @@
+# syntax=docker/dockerfile:1.4
+
 FROM ubuntu:20.04
 
 ARG TARGETOS
 ARG TARGETARCH
 
 ENV DEBIAN_FRONTEND=noninteractive
 ENV DOCKER_COMPOSE_VERSION=1.27.4
-ENV TINI_VERSION=0.19.0
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
     apt-transport-https \
-    curl \
-    ca-certificates \
     bash \
+    ca-certificates \
+    curl \
     git \
     gnupg-agent \
     jq \
     openssh-client \
     perl \
+    python \
+    python3-pip \
     rsync \
     software-properties-common \
+    tini \
     && curl -fsSL https://download.docker.com/linux/ubuntu/gpg | apt-key add - \
     && add-apt-repository \
     "deb [arch=$TARGETARCH] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable" \
     && apt-get update \
     && apt-get install -y --no-install-recommends docker-ce-cli docker-compose-plugin \
-    && rm -rf /var/lib/apt/lists/*
-
-RUN curl -Lfs -o /sbin/tini https://github.com/krallin/tini/releases/download/v${TINI_VERSION}/tini \
-    && chmod +x /sbin/tini \
-    && curl -Lfs https://github.com/docker/compose/releases/download/${DOCKER_COMPOSE_VERSION}/docker-compose-Linux-x86_64 -o /usr/local/bin/docker-compose \
-    && chmod +x /usr/local/bin/docker-compose
+    && rm -rf /var/lib/apt/lists/* \
+    && pip3 install docker-compose==$DOCKER_COMPOSE_VERSION \
+    && apt-get -y purge --auto-remove python3-pip
 
 ENV BUILDKITE_AGENT_CONFIG=/buildkite/buildkite-agent.cfg \
     PATH="/usr/local/bin:${PATH}"

packaging/docker/ubuntu-20.04-linux/entrypoint.sh

@@ -8,4 +8,4 @@ if [[ -d "$DIR" ]] ; then
   /bin/run-parts --exit-on-error "$DIR"
 fi
 
-exec /sbin/tini -- ssh-env-config.sh /usr/local/bin/buildkite-agent "$@"
+exec /usr/bin/tini -- ssh-env-config.sh /usr/local/bin/buildkite-agent "$@"