Docker

Running commands on an image

$ docker run -it --entrypoint sh [imageId] 

Remove all images and containers

#!/bin/bash
# Delete all containers
docker rm $(docker ps -a -q)
# Delete all images
docker rmi $(docker images -q)

source: http://techoverflow.net/blog/2013/10/22/docker-remove-all-images-and-containers/

Docker container sha value

docker inspect --format='{{index .RepoDigests 0}}' <docker-image> 

Remove all images with no tag

REPOSITORY                                                                TAG                 IMAGE ID            CREATED             SIZE
<none>                                                                    <none>              8ad635cb0348        22 hours ago        252.7 MB
<none>                                                                    <none>              2ae831215dd7        40 hours ago        252.7 MB

To remove the images that have no tag, e.g.

docker rmi $(docker images | grep none | awk '{print $3}')

Run an image that was failing

$ docker images
REPOSITORY  TAG                 IMAGE ID            CREATED             SIZE
myimage     1.0.1               bafaeb0cf52a        12 minutes ago      180MB


$ docker run -it --entrypoint sh bafaeb0cf52a

Dockerfile

• https://blog.docker.com/2019/07/intro-guide-to-dockerfile-best-practices/

pulling an image using the sha

docker pull myimage@sha256:0ecb2ad60

Finding the sha256

Getting the sha256 of a docker container 1

docker inspect --format='{{index .RepoDigests 0}}' $IMAGE

Multi-stage builds

## https://quarkus.io/guides/building-native-image#creating-a-container-with-a-multi-stage-docker-build
## Stage 1 : build with maven builder image with native capabilities
FROM quay.io/quarkus/centos-quarkus-maven:19.2.1 AS build
COPY src /usr/src/app/src
COPY pom.xml /usr/src/app
USER root
RUN chown -R quarkus /usr/src/app
USER quarkus
RUN mvn -f /usr/src/app/pom.xml -Pnative clean package

## Stage 2 : create the docker final image
FROM registry.access.redhat.com/ubi8/ubi-minimal
WORKDIR /work/
COPY --from=build /usr/src/app/target/*-runner /work/application
RUN chmod 775 /work
EXPOSE 8080
CMD ["./application", "-Dquarkus.http.host=0.0.0.0"]

mount maven repository

Mount a maven repository using docker buildkit2

on the command line:

export DOCKER_BUILDKIT=1

In the Dockerfile, as the first line

# syntax=docker/dockerfile:experimental

In the Dockerfile, in the mvn run command

RUN --mount=type=cache,target=/root/.m2 \
    mvn --batch-mode -f /usr/src/app/pom.xml clean package

This will look like

Heap dumps from java

Use jattach

apk add --no-cache jattach --repository http://dl-cdn.alpinelinux.org/alpine/edge/community/

Command to use

jattach 1 jcmd "GC.heap_dump /heap.hprof"

• 1. Where can I find the sha256 code of a docker image?, by OhJeez (27 Oct, 2017) stackoverflow ↩

  2. Mounting Volume as part of a multi-stage build, by Marek Obuchowicz (10 Dev, 2018) stackoverflow ↩