Docker run advanced

Docker run command - advanced
=============================

Docker run command...
=====================
 RUN:  - used to run a container
      - will run from local repo, if not it will go to docker hub and pull the image
      onto your local disk drive.
    - If you do a docker run command and the image is not instructed to do anything,
       it will exit immediately, (first download if not on your local machine).
       > this example below will immediately will exit.
docker run unbuntu  (runs version: latests)
  - However if you pass an argument then the image has something to do and will remain
    in operation. For instance:

docker run sleep 1000
 > (1k seconds) which is executing a command on the container.
  OR:

docker run -it centos bash
 > will open container and keep it open
 i.e.- Then you can run a bash command as in: cat /etc/*release*
       > which will show the os and version info.

docker run -d = RUN IN THE BACKGROUND, so you get back to your terminal.

.

For other versions: must specify a tag separated by a colon.
============================================================

docker run ubuntu:17.04    - the version is 17.04.


RUN - Attach and Detach
========================

When you run a container in attach mode it will run in the foreground and display
the results of the container on the screen.
 - You won't be able to see or do anything else on this terminal window until the
   docker container stops.
   Ctrl+C quits the container

docker run <container name>

For Detach mode add the -d option to the docker run command.
================
docker run -d <name of container>

To attach or re-attach - run the docker command with the word attach.
========================
docker attach <name of container>

RUN - STDIN
===========

For a prompt app that asks for name ... if run in docker it will not wait
for standard input.

To run it in Docker: You must map your stdIn off your host to the docker container.
-------------------
using -i parameter...

docker run -i <name of container>

Now the docker container listens on the StdIn of the host (keyboard)

Port mapping
============
- Remember the underlying host where docker is installed is called
"docker host" or "docker engine".
The user accesses the application on the correct port on which Docker is listening.

How docker can be contacted from a web browser...

Two options available:

1. INSIDE the docker host: Use the ip of the docker container. i.e. 172.17.0.2:5000  DEFAULT
   - This is an internal private bridge docker IP accessible within the docker host.
   If you open a browser from inside the docker host you can use:
   TO FIND THE internal IP ADDRESS: RUN THE DOCKER INSPECT COMMAND.
   docker inspect  <container-id>
   > look in the network section of the json near the bottom for the IP address.
      http://172.17.0.2:5000
2. OUTSIDE the docker host: on your local machine. You can use 192.168.1.2 - in this case.

  For the external IP to work you must have mapped a free port inside the docker container to
  the docker host.
  use the -p option e.g.

    docker run -p 80:5000 mmumshad/simple-webapp (name of container image)

    TO FIND THE IP ADDRESS: RUN THE DOCKER INSPECT COMMAND.

   THEN RUN: docker inspect  <container-id> to get the ipaddress and attached the port.

  You can run multiple instances of on application and map them to different ports on the docker host.

    docker run -p 8080:5000 mmumshad/simple-webapp (name of container image)

  or you can run different instances of different applications

    docker run -p 3306:3306 mysql

  and another instance of mysql on a different port.

    docker run -p 8306:3306 mysql

YOU CANNOT map the same port on the docker host to more than one container.

Docker Run - Volume mapping (for persistence)
===========================
 - How data is persisted in Docker containers.

docker run mysql

The mysql data is stored inside the container by default at:
 /var/lib/mysql

 - as soon as you delete the container you lose all the data.
 To persist the data you would want to map a directory outside the docker container
 on the docker host to a directory inside the docker container.

docker run -v /opt/datadir:/var/lib/mysql mysql
              host dir          container dir
 - this way when the docker container runs it will implicitly mount the external directory
   to the directory inside the docker container.
   The data will remain even if you delete the docker container.

The next time you run the mysql container map it to the data directory on the host and all the
data will be available.











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