docker-alpine-init

Provides s6 init system via s6-overlay in addition to that provided by robwdux/alpine-base

See below for help with the s6 init system

Addons available selectively during build. Assisting applications include:

• telegraf for exporting metrics (e.g. read a stats endpoint and stream to influxdb or another of the supported outputs)
• consul-template for dynamic configuration (requires consul)

Alpine Linux base image plus s6 init system

Control the initialization, runtime and shutdown of containers through multi stage init.

• process supervision, especially for assisting processes
• reap defunct "zombie" processes (specifically for applications that spawn additional processes), mitigating a full process table

3 Stage Init system

Stage 1:

• s6-init setup

Stage 2:

• container initialization - execute code prior to starting services, e.g. apply runtime configuration
• process supervision - start and supervise defined services under the service directory

Stage 3:

• container shutdown - execute code prior to service(s) being stopped

...start your Dockerfile

FROM robwdux/alpine-init

Processes should not daemonize, but run in foreground under supervision of the init system

Processes should log to standard error and standard out

Leverage the docker log driver to stream logs off the host without incurring the i/o hit on disk.

Test Drive, Iterate for a new image

Interactively test commands and such then record in a Dockerfile for a new project

Build or run with docker-compose

# add short alias for docker-compose
echo "alias dc='docker-compose '" >> ~/.bashrc && source ~/.bashrc

# the repo
git clone https://github.com/robwdux/docker-alpine-init.git

cd docker-alpine-init/

# build and run (image doesn't exist locally)
dc run --rm -ti init bash

# build explicitly
dc build

# build with meta data via build args for git info
sudo ./build.sh

# view meta data
$ docker inspect --format '{{ json .Config.Labels }}' robwdux/alpine-init:1.18.3.1 | jq

shell in interactively

sudo docker run --rm -it \
                   --name init \
                   robwdux/docker-alpine-init \
                   sh

shell into a daemonized running container

sudo docker run -d \
                --name init \
                robwdux/docker-alpine-init \
                ping 8.8.8.8 && \
sudo docker exec -it init sh

# in container
bash-4.3# ps
PID   USER     TIME   COMMAND
    1 root       0:00 s6-svscan -t0 /var/run/s6/services
   21 root       0:00 foreground  if   /etc/s6/init/init-stage2-redirfd   foreground    if     if      s6-echo      -n      --      [s6-init] making
   22 root       0:00 s6-supervise s6-fdholderd
   26 root       0:00 foreground  s6-setsid  -gq  --  with-contenv  ping  8.8.8.8  import -u ? if  s6-echo  --  ping exited ${?}  foreground  redirfd
   99 root       0:00 /bin/busybox ping 8.8.8.8
  100 root       0:00 bash
  106 root       0:00 ps

bash-4.3# ps -o user,group,comm,pid,ppid
USER     GROUP    COMMAND          PID   PPID
root     root     s6-svscan            1     0
root     root     foreground          21     1
root     root     s6-supervise        22     1
root     root     foreground          26    21
root     root     busybox             99    26
root     root     bash               100     0
root     root     ps                 105   100

Customization

Working with Alpine Linux overview

Working with s6 init system

• Getting Started

• Project source repo and doc used for this container

• s6 Official Information

• Docker and s6