Add a Prometheus exporter, use s6

Dockerfile

-FROM debian:stable-slim
+FROM debian:stable-slim AS exporter_build
 
-COPY build.sh /tmp/build.sh
+WORKDIR /tmp
+RUN apt-get -q update && \
+    env DEBIAN_FRONTEND=noninteractive apt-get -y install --no-install-recommends curl ca-certificates
 
-RUN /tmp/build.sh && rm /tmp/build.sh
+RUN MEMCACHED_EXPORTER_VERSION=0.10.0 && \
+    curl -vsfL https://github.com/prometheus/memcached_exporter/releases/download/v${MEMCACHED_EXPORTER_VERSION}/memcached_exporter-${MEMCACHED_EXPORTER_VERSION}.linux-amd64.tar.gz | tar xzf - && \
+    cp memcached_exporter-${MEMCACHED_EXPORTER_VERSION}.linux-amd64/memcached_exporter /usr/bin/memcached_exporter && \
+    rm -fr memcached_exporter*
 
-ENTRYPOINT ["/bin/sh", "-c", "/usr/bin/memcached -m ${MEM:-64} -c ${MAXCONN:-16384} -p ${PORT:-11211} ${ENABLE_SASL:+-S}"]
+FROM registry.git.autistici.org/ai3/docker/s6-base:master
+
+RUN apt-get -q update && \
+    env DEBIAN_FRONTEND=noninteractive apt-get -y install --no-install-recommends curl memcached && \
+    apt-get clean && \
+    rm -fr /var/lib/apt/lists/*
+
+COPY --from=exporter_build /usr/bin/memcached_exporter /usr/bin/memcached_exporter
+COPY services.d/ /etc/services.d/
 

README.md

@@ -10,3 +10,6 @@ The server can be configured with environment variables:
 (a valid */etc/sasldb2* should be mounted into the container for it
 to work).
 
+The container will run a Prometheus exporter on PORT + 1, this can
+be overridden with the `EXPORTER_PORT` environment variable.
+

build.sh

-#!/bin/sh
-#
-# Install script for memcached inside a Docker container.
-#
-
-# The default bitnami/minideb image defines an 'install_packages'
-# command which is just a convenient helper. Define our own in
-# case we are using some other Debian image.
-if [ "x$(which install_packages)" = "x" ]; then
-    install_packages() {
-        env DEBIAN_FRONTEND=noninteractive apt-get install -qy -o Dpkg::Options::="--force-confdef" -o Dpkg::Options::="--force-confold" --no-install-recommends "$@"
-    }
-fi
-
-die() {
-    echo "ERROR: $*" >&2
-    exit 1
-}
-
-set -x
-
-apt -q update
-
-# Install memcached.
-install_packages memcached \
-    || die "could not install packages"
-
-# Clean up.
-apt-get autoremove -y
-apt-get clean
-rm -fr /var/lib/apt/lists/*

services.d/exporter/run

+#!/bin/sh
+
+default_exporter_port=$(expr ${PORT:-11211} + 1)
+exec /usr/bin/memcached_exporter --memcached.address=127.0.0.1:${PORT:-11211} --web.listen-address=:${EXPORTER_PORT:-${default_exporter_port}}
+

services.d/memcache/finish

+#!/usr/bin/execlineb -S0
+
+s6-svscanctl -t /var/run/s6/services

services.d/memcache/run

+#!/bin/sh
+
+exec /usr/bin/memcached -m ${MEM:-64} -c ${MAXCONN:-16384} -p ${PORT:-11211} ${ENABLE_SASL:+-S}
+