Adding a deploy hook

Overview

Deploy hooks are scripts that allow you to automate actions at various points during the deployment process for your applications. This allows you to customise your deployments by, for example, installing software packages or upgrading components.

We will be looking at some simple examples in this tutorial, but for a deeper understanding please read the full reference guide.

What you’ll need

Before you start, please check you have the following:

Creating a deploy hook

Deploy hooks can be added to an application via the Dashboard. Like most other configuration templates in Maestro, Deploy hooks are YAML-formatted.

A deploy hook needs, at a minimum:

So, to write a deploy hook we must:

  1. Choose your environment - eg. example production, development, staging and so on.
  2. Define your hook point - eg. first_thing
  3. Define your hook type i.e. snippet, command or script.
  4. Define your target
  5. Define the hook fields you require.

Writing the YAML

The simplest kind of hook is the command. This simply executes a command in the operating system as part of the deployment process.

We’re going to add the hook below to our demo application:

production: # Environment
    first_thing: # Hook point
      - command: apt-get install nmap -y # Hook type
        target: any # Hook fields
        execute: true

This hook will install the nmap package on our server during the deployment process. We’ve added the execute hook field because we want the command to be executed during deployment. If you don’t add this field, the code you’re calling won’t be executed.

Important

When automating the installation of packages, remember to use the -y flag to answer yes to all prompts.

Adding the hook to your app

Hooks can be added to an application in one of two ways:

We’re going to use the first method in our tutorial because it’s quicker and simpler.

To add the hook:

  1. Open the Application Overview from your Dashboard
  2. Click on Configuration files in the Application panel on the right of the screen
  3. Click on the Deploy Hooks tab at the top of the Configure Services
  4. Copy and paste the example code above into the text area
  5. Click Preview and then check there are no errors in the parsed template file
  6. Add a commit message and click Commit to server

Deploying and testing

Now that our hook is in place, we need to re-deploy our application to see it in action.

  1. Navigate back to Application Overview
  2. Click the Build / Deploy button
  3. Watch the deploy log and you will see the “first _thing” deploy hook being called as part of the process

The best way to check whether your change has been applied to your server is to access it directly using SSH. Cloud 66 Toolbelt is the quickest way to do this.

Once you are connected to your server, type nmap into the terminal. If your deploy hook was set up correctly, you will see the usage / help text for the nmap utility. If not, Ubuntu will complain that nmap is not installed.

Understanding hook points and ordering

Hook points are used to define the point in your deployment process at which a hook should be invoked. This is obviously critical when there are tight dependencies between the components of your application (i.e. one component relies on another component being installed first), but it is also important in terms of what actions and commands are possible. For example, running tasks against a database before the database server is installed will not work!

It’s important to understand the order in which hook points will occur in the flow of deployment. The simplified deployment process below shows where each deploy hook is triggered. Hooks are marked in bold italic. Some hooks have several possible values (x, y, z). Click on the hook name to see a list of available options:

Deployment process (simplified)

  1. Server is fired up
  2. Operating system and standard system components installed → first_thing
  3. before_agent → Cloud 66 Agent is installed → after_agent
  4. before_x → Database is installed → after_x
  5. before_y → Database replication is configured → after_y
  6. before_data_mount → Data is mounted → after_data_mount (GlusterFS specific)
  7. custom_server (runs on custom servers only)
  8. before_nginx → NGINX is installed → after_nginx
  9. before_docker → Docker is installed after_docker
  10. last_thing

Notes

Using snippets

Snippets are pre-defined hook scripts hosted in a Cloud 66 repository. These are commonly used scripts that we provide for ease of use. Like scripts (see below) these snippets are written in bash.

For example the Cloud 66 ImageMagick snippet installs ImageMagick, the popular image processing application. You can use the example below to test it in your demo app:

production: # Environment
    first_thing: # Hook point
      - snippet: cloud66/imagemagick # Hook type
        target: any # Hook fields
        execute: true

You can test this in the same way as you did with the command hook above.

Using inline scripts

Script hooks allow you to add your own logic to a deploy hook, either by calling a separate file using source or by using inline. Both of methods use bash scripting (as do snippets above).

The hook below will create an arbitrary log file in /tmp using a simple inline script:

first_thing: # Hook point
 - inline: |

     #!/usr/bin/env bash
     echo "script called!" >> /tmp/inline_script.log
   target: any
   execute: true
   apply_during: all
   owner: root:root

What’s next

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