Problem with Docker Persistence

• Lets try to understand two kinds of applications

  • Stateless:
    • Which doesn’t use the local storage to store details
    • eg: Web Server
  • Stateful:
    • They use local storage to store necessary information
    • eg: Database

• We have to preserve the writable layers which are deleted when container is removed/terminated

• To Preserve the writable layer. Writable layer needs to be present in the Docker Host even after container is deleted.

• Preserving the writable layer after container is terminated can be acheived by using

  • Bind mount
  • Volume
  • tmpfs
  • namedpipe

• Refer here for complete info.

Docker Volumes

• Volume will become a mount in the container.
• Lifecycle of container will not impact Volume.
• How can we create volume
  • Dockerfile:
    • Inside Dockerfile we have a instruction VOLUME
  • Using Docker CLI:
    • Create docker volumes by using docker volume
    • -v
    • –mount
    • For this section use examples mentioned here
• Dockerfile Example:

FROM ubuntu:18.04
LABEL AUTHOR="khaja"
LABEL ORG="QT"
RUN apt-get update && apt-get install openjdk-8-jdk -y && mkdir /myapp
VOLUME /myapp
ADD https://qt-s3-new-testing.s3-us-west-2.amazonaws.com/spring-petclinic.jar  /myapp/spring-petclinic.jar
# COPY ./spring-petclinic.jar  /spring-petclinic.jar
EXPOSE 8080
CMD ["java", "-jar", "/myapp/spring-petclinic.jar"]

• Terms to know

  • Named Volume:

  docker volume create myvol
  # use this
  docker container run -d -v myvol:/tools alpine sleep 1d
  

  • Anonymous Volume:
    • From Dockerfile
    • From commandline if -v option has no name attached docker container run -d -v /tools alpine sleep 1d

How to store volume Data outside of Docker Host

• Refer Here for network file system as docker volume