Create an addon

This tutorial guides you through the creation of a simple addon. The addon that we create in this tutorial is an example for enabling SSH access on a container.

1. Write the addon metadata

In a new ssh-addon directory, create a manifest.yaml file with the following content:

name: ssh
description: |
  Enable SSH access when starting a container

2. Add a hook

Next to your manifest.yaml file in the ssh-addon directory, create a hooks directory. This is where we’ll put the hooks we want to implement.

Hooks can be implemented in any language, but we are using a bash script here.

In the hooks directory, create a pre-start file with the following content:

#!/bin/bash

if [ "$CONTAINER_TYPE" = "regular" ]; then
  exit 0
fi

mkdir -p ~/.ssh
cat "$ADDON_DIR"/ssh-addon-key.pub >> ~/.ssh/authorized_keys

Make the file executable. To do so, enter the following command (in the ssh-addon directory):

chmod +x hooks/pre-start

Create an SSH key in your addon directory and move the private key to a location outside of the addon directory (for example, your home directory):

ssh-keygen -f ssh-addon-key -t ecdsa -b 521
mv ssh-addon-key ~/

Alternatively, you can use an existing key and move the public key into the addon directory.

3. Create the addon

Your addon structure currently looks like this:

ssh-addon
├── hooks
│   └── pre-start
├── manifest.yaml
└── ssh-addon-key.pub

Create the addon with amc by entering the following command (in the directory that contains the ssh-addon directory):

amc addon add ssh ./ssh-addon

When your addon is created, you can view it with:

amc addon list

4. Use the addon in an application

Create an application manifest file (my-application/manifest.yaml) and include the addon name under addons:

name: my-application
instance-type: a4.3
addons:
  - ssh

Then create your application:

application_id=$(amc application create ./my-application)
amc wait "$application_id" -c status=ready

The amc wait command returns when your application is ready to launch. You can now launch an instance of your application:

amc launch my-application --service +ssh

The SSH port 22 is closed by default. In the above command, we open it by exposing its service by using --service.[/note]

You can now access your container via SSH:

ssh -i ~/ssh-addon-key root@<container_ip> -p <exposed port>

More information

• Addon reference
• How to update addons
• Extend an application

Last updated 4 months ago.