Using tasks and hooks

Defining tasks

Tasks are basically functions defined within Bootleg configuration files to accomplish one or more goals in the deployment process.

Example - Clear an application cache

use Bootleg.DSL

task :clear_cache do
  UI.puts "Clearing cache"
  remote :app do
    "rm /opt/app/cachefile"
  end
end

Here we define a task that will run a command on all :app servers.

Existing tasks, including those that come with Bootleg, can be redefined by you as needed.

Redefining a built-in task

```elixir tab="Config" use Bootleg.DSL task :build do UI.info("Doing our own thing!") end

```bash tab="Output"
$ mix bootleg.build
Warning: task 'build' is being redefined. The most recent definition will be used.
To prevent this warning, set `override: true` in the task options. The previous
definition was at: path/to/bootleg/lib/bootleg/tasks/build.exs:13
Doing our own thing!

In order to squelch the warning that a task is being overridden, you may supply override: true to the task macro:

Redefining a built-in task without triggering a warning

```elixir tab="Config" use Bootleg.DSL task :build, override: true do UI.info("Doing our own thing!") end

```bash tab="Output"
$ mix bootleg.build
Doing our own thing!

Running tasks

Invoking tasks from the command line

Bootleg comes with several Mix tasks, but the one we'll show you here is called invoke.

Using bootleg.invoke

$ mix bootleg.invoke foo
Clearing cache
...[snip]

The result of the command having been run on the :app servers would appear here.

Invoking tasks from other tasks

Tasks can invoke other tasks.

```elixir tab="Config" use Bootleg.DSL

task :one do invoke :two end

task :two do UI.puts "tada!" end

```bash tab="Output"
$ mix bootleg.invoke one
tada!
$ mix bootleg.invoke two
tada!

Invoking a task will also invoke any tasks that have been registered to run as hooks before/after that task.

Note

Invoking an undefined task is not an error and any registered hooks for that task will still be executed.

Using hooks

In addition to being run from tasks, tasks can be set to run before or after other tasks.

Defining hooks for arbitrary tasks

Hooks can be defined for any task (built-in or user defined), even those that do not exist. This can be used to create an "event" that you want to respond to, but has no real "implementation".

Future proofed

use Bootleg.DSL

before_task :the_big_one do
  IO.puts "it's time to get outta here!"
end

This is valid even though there is no task registered with the name :the_big_one.

Hooking into built-in Bootleg tasks

Much of Bootleg is written using Bootleg tasks. This means you can hook into many different parts of the build and deployment process.

Notifying an external service

use Bootleg.DSL

before_task :build do
  MyAPM.notify_build()
end

after_task :deploy do
  MyAPM.notify_deploy()
end

For a list of tasks that you can hook into, refer to the workflows.

Defining multiple hooks for the same task

You can define multiple hooks for a task, and they will be executed in the order they are defined.

Using multiple hooks

```elixir tab="Config" use Bootleg.DSL

before_task :start do IO.puts "This may take a bit" end

after_task :start do IO.puts "Started app!" end

before_task :start do IO.puts "Starting app!" end

```bash tab="Output"
$ mix bootleg.invoke start
This may take a bit
Starting app!
Started app!

When invoking a task, the order in which hooks have been defined for that task is respected.