*`docker-get-image` - Return sha256 of the image used by the docker.
*`docker-get-status` - Return the status of the docker.
*`docker-log-cleanup` - Empty the file logging the docker output on the docker host.
*`docker-log-truncate` - Truncate the file logging the docker output on the docker host.
*`docker-run` - Run a docker, reading options to pass to the `docker run` command from a Dockeropts file.
### Build a docker image
On the docker hosts, you'll be able to build docker images and run dockers, based on Dockerfile and Dockeropts files located in the /etc/docker subdirectories.
To create an `nginx` docker image, create a directory /etc/docker/nginx with a Dockerfile and a Dockeropts files into.
``` bash
# mkdir -p /etc/docker/nginx
# cat << EOF > /etc/docker/nginx/Dockerfile
FROM nginx:alpine
EOF
# cat << EOF > /etc/docker/nginx/Dockeropts
DOCKER_ULIMIT="nofile=65536"
DOCKER_PORT="80:80"
EOF
```
Build your `nginx` docker image, then run it ! The docker-run command will read the Dockeropts file to add the --ulimit and --port options to the docker run command.
``` bash
# docker-build nginx && docker-run nginx
```
### Override your files
If you want to copy a file in your Dockerfile, say the default nginx.conf, you can use the DOCKER_BUILD_PREFIX and DOCKER_BUILD_SUFFIX variables to get different versions of this file giving some context.
You can now override the nginx configuration file when you build your image.
* Without option, the docker-build command will search for the file beside your Dockerfile.
``` bash
# docker-build nginx && docker-run nginx
```
Both DOCKER_BUILD_PREFIX and DOCKER_BUILD_SUFFIX variables are empty, the Dockerfile will search for a `./nginx.conf` file, ie the /etc/docker/nginx/nginx.conf file.
* With a -c|--cluster option, the docker-build command will search for the file in a subdirectory below your Dockerfile.
The DOCKER_BUILD_PREFIX variable is populated with 'custom/' to force the Dockerfile to search for a `./custom/nginx.conf` file, ie /etc/docker/nginx/custom/nginx.conf file.
The DOCKER_BUILD_PREFIX variable is populated with 'custom/' and the DOCKER_BUILD_SUFFIX variable is populated with '-develop' to force the Dockerfile to search for a `./custom/nginx.conf-develop` file, ie /etc/docker/nginx/custom/nginx.conf-develop file.
### Override your options
The same override principle can be used for the Dockerfile and the Dockeropts file when using the docker-build and docker-run commands.
You can create a /etc/docker/nginx/custom/Dockeropts file that would override your default Dockeropt file, and a /etc/docker/nginx/custom/Dockeropts-develop file overriding both other files too.
The Dockeropts file accepts the following options.
*`SYSCTL` - values to set on the docker host via the sysctl command before running the docker
*`DOCKER_ARGS` - values to pass to the docker build command with --build-arg options
*`DOCKER_ENV` - values to pass to the docker run command with -e options
*`DOCKER_LINK` - values to pass to the docker run command with --link options
*`DOCKER_OPT` - values to pass to the docker run command with prefixed by --
*`DOCKER_PORT` - values to pass to the docker run command with -p options
*`DOCKER_ULIMIT` - values to pass to the docker run command with --ulimit options
*`DOCKER_VOLUME` - values to pass to the docker run command with -v options
*`HOST_VOLUME` - volumes to allow write access to from the docker on selinux enabled host
Overriding options is done several times, reading options from the more specific to the more generic file. In our example, files are read in this order :
Following configuration builds and runs the docker image 'nginx-develop' for the 'custom' cluster described in our example.
The Dockerfile and Dockeropts files needed in the /etc/docker/nginx directory should be present on the docker host, likely synchronised by an other ansible role.
