Abstract
This article contains information about Docker for Developers in a compact format.
The following solutions have been tested on POSIX compatible OS machines running MacOS, CentOS and Ubuntu. They should work on Windows in a PowerShell as well.
Problem & Solution
Clean & Reset Docker
docker system prune -a
Delete all Docker containers
docker rm $(docker ps -a -q)
Remove a single Docker image
docker rmi <imageId>
Load a Docker image into the local repository
docker load -i services.img
Export a Docker image from local repository to the host file system
docker save - i services.img
Fetch a Docker image from a (remote) repository
docker pull <vendorTag>:<imageId>
List all installed Docker Images
docker images -a
List all running Docker containers
docker ps -a
Create a GeoJSON Dumpfile using GDAL via Docker
Pull the GDAL image.
docker pull osgeo/gdal:ubuntu-small-latest
Run ogr2ogr to fetch the DB records by using the given SQL Statement and convert them using the GeoJSON driver. The result is saved as the given file into the container’s /home path, that is actually mapped to the /home path of the host. You can change the mapped path to whatever host directory you want. The “–rm” parameter will let Docker remove the container runtime instance straight after use, to save some resources.
docker run --rm -v /home:/home osgeo/gdal:ubuntu-small-latest ogr2ogr -f "GeoJSON" "/home/geojson-export-limited.json" PG:"host=<ip> dbname='<db_name>' user='<db_user>' password='<db_user_password>'" -sql "select * from <db-table> order by <pkey> asc limit <size_limit>"
Usage of Docker Compose to build a service stack using multiple containers
- Create a docker-compose.yml file to specify the stack
- Trigger a build, using the following command while being in the directory with the docker-compose.yml file:
docker-compose build
Usage of Docker Compose to start a service stack using multiple containers
Run the following command within the directory of the corresponding docker-compose.yml file. Skip parameter “-d” if you want immediate logging output to the stdout.
docker-compose up -d
Run the following command if you need to recreate the containers at startup.
docker-compose up -d --force-recreate
Usage of Docker Compose to stop a service stack using multiple containers
Run the following command within the directory of the corresponding docker-compose.yml file.
docker-compose down
Usage of Docker Compose to follow the logs of a service stack’s running docker containers
Run the following command within the directory of the corresponding docker-compose.yml file.
docker-compose logs -f
Usage of Docker Compose to follow the logs of one container in a service stack
Run the following command within the directory of the corresponding docker-compose.yml file.
docker-compose logs pump <container-name>
Enable Docker Swarm Mode
Docker Swarm is a mechanism to distribute and orchestrate containers over more than one machine node. You can easily build a simple server cluster with neat cloud semantics without any programming hac-mac, just by using preconfigured base images with corresponding applications.
A simple load balancing mechanism will also take place, just like using Spring Cloud Netflix Eureka Discovery Service. However using Docker Swarm mode the load balancing will take place not on application level, but on the “system” level. If you need fine control and discovery features within the service stack and you should also use the Eureka way, though. Whereas Docker swarm simply eases the pain about cluster orchestration (ie. distributed deployments).
Eureka vs Docker Swam (redundancies)
In swarm mode Docker Compose is used to configure the actual service stack, just like in a single node environment.
The master / manager node is initialised using the following command:
docker swarm init --advertise-addr <MANAGER-IP>
To let a node join the swarm the above command will print out information of how to do it. Example:
Swarm initialized: current node (dxn1zf6l61qsb1josjja83ngz) is now a manager.
To add a worker to this swarm, run the following command:
docker swarm join \
--token SWMTKN-1-49nj1cmql0jkz5s954yi3oex3nedyz0fb0xx14ie39trti4wxv-8vxv8rssmk743ojnwacrr2e7c \
192.168.99.100:2377If you want to test a single node swam you can omit the manager node’s ip and use this command:
docker swarm init
Deploy a Docker Compose stack to Docker in swarm mode
To deploy a Docker Compose stack to Docker in swarm mode use the following command:
docker stack deploy --compose-file docker-compose.yml <stack_name>
Display information about a Docker Swarm
docker info
Display information about nodes of a Docker swarm
docker nodes ls
