Docker experiment to build hello world image from scratch. Instead of using shell script, C based application is used to make it comparable to custom application package/distribution.
Creating minimal docker image
what you need :
docker installed on linux variant (tested on Ubuntu 14LTS)
gcc for making minimal application
docker can import archives such as tar, tar.gz, .bzip etc. you can package all necessary files into an archive and import it into docker.
tar cv --files-from /dev/null | sudo docker import - empty
This will create empty image in docker repository.
Now lets create Helloworld application to package it to docker.
file: a.c
#include<stdio.h>
void main() {
printf("Hello from docker!!\n");
}
We can compile with static linking to avoid shared library dependencies.
gcc -static a.c -o a`
Verify that there are not dependencies with ldd
ldd "a"
> not a dynamic executable
Create a Dockerfile with below entries (configuration for docker container that we are about to build).
FROM empty
ADD ./a /a
CMD ["/a"]
It says docker that seed the image from empty image that we have created and add file a
to it as target path /a and startup command is to execute /a
Now build the image with
$ sudo docker build -t "first_image" ./
Sending build context to Docker daemon 880.6 kB
Sending build context to Docker daemon
Step 0 : FROM empty
---> 62f67e5fbc6a
Step 1 : ADD ./a /a
---> 1236c4ce0129
Step 2 : CMD ["/a"]
---> f6982bf61e13
Successfully built f6982bf61e13
Now you can list images with
$sudo docker images
REPOSITORY TAG IMAGE ID CREATED VIRTUAL SIZE
first_image latest 9ba228119b81 54 seconds ago 877.4 kB
To Run the docker instance in background mode :
$ sudo docker run first_image
You should see output like
Hello from docker
Recommended to checkout https://github.com/docker/docker.git and browse the source in your favorite ide