Quick Guide To Docker

What is docker?

Docker provides a virtualization environment to run containers. In more practical terms it means we can define docker images that run on top of the OS virtualization to provide services. A container is in principle the instance of the image.

Docker Terminology Definitions

Docker image

A docker image is a set of services defined to run on top of the Virtual Host OS.

Dockerfile

A file containing a docker image definition ex.

# define the base image to pull
FROM docker.elastic.co/elasticsearch/elasticsearch:7.10.2
# make port 9200 and 9300 available to the world outside this container
EXPOSE 9200
EXPOSE 9300

Add the above to a file named "dockerfile" in the root of a folder called my_elastic_image and we can build the image with;

# build the image file
$ docker build ./my_elastic_image --tag=mbister/elastic_cust
# run the custom image file
$ docker run -d -p 9200:9200 -p 9300:9300 -e "discovery.type=single-node" mbister/elastic_cust

This is how simple it is to pull the base of of ubuntu and start building a custom image

FROM ubuntu:latest
# Update the image to the latest packages
RUN apt-get update && apt-get upgrade -y

Docker compose

With docker-compose and a docker-compose.yml file we can define and run multiple container services. For example, we can fire up Kibana and Elastic in one composition.

version: '3'
services:
elasticsearch:
image: docker.elastic.co/elasticsearch/elasticsearch:7.10.2
environment:
- cluster.name=docker-cluster
- bootstrap.memory_lock=true
- "ES_JAVA_OPTS=-Xms512m -Xmx512m"
ulimits:
memlock:
soft: -1
hard: -1
ports:
- "9200:9200"
kibana:
image: docker.elastic.co/kibana/kibana:7.10.2
ports:
- "5601:5601"

We can run the above file by;

# run the docker-compose file in the background (-d)
$ docker-compose up -d
# specifying the docker-compose file
$ docker-compose -f <compose_file> up -d

We can now access Kibana on http://localhost:5601/ and ES on http://localhost:9200/. To shutdown we use the down option;

$ docker-compose down

If you just want to fire up a container with out much fuzz;

$ sudo docker pull docker.elastic.co/elasticsearch/elasticsearch:7.10.2
$ sudo docker run -p 9200:9200 -p 9300:9300 -e "discovery.type=single-node" --name "es_demo_app" docker.elastic.co/elasticsearch/elasticsearch:7.10.2

The 'p' flag sets the port forwarding to the container, from local to container.

The 'e' flag sets elastic to a single node mode.

The --name flag is used to give it a handy name and it will ensure we start the same container with data persistency.

Start by using the name.

#start
$ docker container run es_demo_app

Stop by using the name.

#stop
$ docker container stop es_demo_app

List containers

$ docker container ls

List running containers

$ docker container ps

Tricks and treats.

A handy way of removing all containers

#-a all -q ids
$ docker container rm $(docker container ls -a -q)

A super handy little trick if your container crashes or causes other issues, you can access the terminal on the docker image:

$ docker exec -it <containerid> /bin/bash