init

Dockerfile

@@ -0,0 +1,44 @@
+# Use Alpine as the base image
+FROM alpine:3.20.2
+
+# Install necessary packages & Go
+RUN apk add --no-cache \
+    alpine-base \
+    logrotate \
+    dcron \
+    go \
+    s6-overlay
+
+# Set up the s6-overlay configuration
+COPY etc /etc
+
+# Set up Go environment
+ENV GOPATH /go
+ENV PATH $GOPATH/bin:/usr/local/go/bin:$PATH
+
+# Copy the Go application
+COPY main.go /app/main.go
+
+# Build the Go application
+RUN go build -o /usr/local/bin/myapp /app/main.go
+
+# Set up syslog
+#COPY syslog.conf /etc/syslog.conf
+#RUN mkdir -p /var/log/syslog
+
+# Set up logrotate
+#COPY logrotate.conf /etc/logrotate.conf
+
+# Set up watchdog
+#COPY watchdog.conf /etc/watchdog.conf
+
+# Copy your application
+# COPY myapp /usr/local/bin/myapp
+
+# Set up s6 service for your app
+#COPY run /etc/services.d/myapp/run
+
+ENV LOG_LEVEL=WARNING
+
+# Use s6-overlay as the entrypoint
+ENTRYPOINT ["/init"]

README.md

@@ -0,0 +1,17 @@
+# Alpine with S6-Overlay
+
+I want a docker image that behaves more like a VM:
+
+1. I can start / stop many processes, also the main process (usually PID 1)
+   Why? To test things out. Changing environment variables, debugging with the coredump file or recompiling the app without crashing the container follows much more my development process
+2. Logging to a seperate file with logrotation
+   Why? Docker logs (and Kibana) are a pain in the ass!
+3. Watchdog: k8s restarts containers when they are crashing. That should be done by the s6-overlay.
+
+## Tested
+
+- [x] Starting & Stopping services with `s6-rc start myapp` and `s6-rc stop myapp`
+- [x] `docker exec` into the container and run myapp manually, it uses the env vars of the shell
+- [x] Logging: `/var/log/myapp/current` is filled
+- [ ] Logrotation
+- [ ] Cron

etc/s6-overlay/s6-rc.d/myapp-log-prepare/type

@@ -0,0 +1 @@
+oneshot

etc/s6-overlay/s6-rc.d/myapp-log-prepare/up

@@ -0,0 +1,3 @@
+if { mkdir -p /var/log/myapp }
+if { chown nobody:nogroup /var/log/myapp }
+chmod 02755 /var/log/myapp

etc/s6-overlay/s6-rc.d/myapp-log/consumer-for

@@ -0,0 +1 @@
+myapp

etc/s6-overlay/s6-rc.d/myapp-log/pipeline-name

@@ -0,0 +1 @@
+myapp-pipeline

etc/s6-overlay/s6-rc.d/myapp-log/run

@@ -0,0 +1,2 @@
+#!/bin/sh
+exec logutil-service /var/log/myapp

etc/s6-overlay/s6-rc.d/myapp-log/type

@@ -0,0 +1 @@
+longrun

etc/s6-overlay/s6-rc.d/myapp/finish

@@ -0,0 +1,9 @@
+#!/bin/sh
+
+if test "$1" -eq 256 ; then
+  e=$((128 + $2))
+else
+  e="$1"
+fi
+
+echo "$e" > /run/s6-linux-init-container-results/exitcode

etc/s6-overlay/s6-rc.d/myapp/producer-for

@@ -0,0 +1 @@
+myapp-log

etc/s6-overlay/s6-rc.d/myapp/run

@@ -0,0 +1,3 @@
+#!/command/with-contenv sh
+exec 2>&1
+exec s6-setuidgid daemon /usr/local/bin/myapp

etc/s6-overlay/s6-rc.d/myapp/type

@@ -0,0 +1 @@
+longrun

go.mod

@@ -0,0 +1,3 @@
+module example.com/loglevel
+
+go 1.22.3

main.go

@@ -0,0 +1,26 @@
+package main
+
+import (
+	"log"
+	"os"
+	"time"
+)
+
+func main() {
+	// Configure logging to include timestamp
+	log.SetFlags(log.Ldate | log.Ltime | log.Lmicroseconds)
+
+	// Read LOG_LEVEL from environment variable
+	logLevel := os.Getenv("LOG_LEVEL")
+	if logLevel == "" {
+		logLevel = "INFO" // Default log level
+	}
+
+	log.Printf("Starting application with LOG_LEVEL: %s", logLevel)
+
+	// Infinite loop to log every 2 seconds
+	for {
+		log.Printf("Current LOG_LEVEL: %s", logLevel)
+		time.Sleep(2 * time.Second)
+	}
+}

run

@@ -0,0 +1,7 @@
+#!/usr/bin/with-contenv sh
+
+# Start your application
+exec /usr/local/bin/myapp
+
+# Touch the watchdog file
+touch /var/run/myapp.touch