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Expand Up @@ -4,11 +4,11 @@ title: Ansible Intermediate

# Ansible Intermediate

In this chapter you will continue to learn how to work with Ansible.
In this chapter, you will continue to learn how to work with Ansible.

****

**Objectives**: In this chapter you will learn how to:
**Objectives**: In this chapter, you will learn how to:

:heavy_check_mark: work with variables;
:heavy_check_mark: use loops;
Expand All @@ -24,9 +24,9 @@ In this chapter you will continue to learn how to work with Ansible.

****

In the previous chapter, you learned how to install Ansible, use it on the command line, or how to write playbooks to promote the re-usability of your code.
In the previous chapter, you learned how to install Ansible, use it on the command line, and write playbooks to promote the re-usability of your code.

In this chapter, we can start to discover some more advanced notions of how to use Ansible, and discover some interesting tasks that you will use very regularly.
In this chapter, we can start to discover more advanced notions of how to use Ansible and some interesting tasks that you will use regularly.

## The variables

Expand All @@ -45,7 +45,7 @@ These variables can be organized as:
* dictionaries,
* lists.

A variable can be defined in different places, like in a playbook, in a role or from the command line for example.
A variable can be defined in different places, such as a playbook, a role, or the command line.

For example, from a playbook:

Expand Down Expand Up @@ -148,13 +148,13 @@ Use of a stored variable:

!!! Note

The variable `homes.stdout_lines` is a list of variables of type string, a way to organize variables that we had not yet encountered.
The variable `homes.stdout_lines` is a list of variables of type string, a way to organize variables we had not yet encountered.

The strings that make up the stored variable can be accessed via the `stdout` value (which allows you to do things like `homes.stdout.find("core") != -1`), to exploit them using a loop (see `loop`), or simply by their indices as seen in the previous example.

### Exercises-1
### Exercises:

* Write a playbook `play-vars.yml` that prints the distribution name of the target with its major version, using global variables.
* Write a playbook, `play-vars.yml,` using global variables that print the target's distribution name and major version.

* Write a playbook using the following dictionary to display the services that will be installed:

Expand All @@ -176,13 +176,13 @@ The default type should be "web".

## Loop management

With the help of loop, you can iterate a task over a list, a hash, or dictionary for example.
A loop allows you to iterate a task over a list, a hash, or a dictionary, for example.

!!! Note

More information can be [found here](https://docs.ansible.com/ansible/latest/user_guide/playbooks_loops.html).

Simple example of use, creation of 4 users:
A simple example of use, creation of 4 users:

```bash
- name: add users
Expand All @@ -209,7 +209,7 @@ users:
- xavier
```

and be used inside the task like this (after having include the vars file):
and be used inside the task like this (after having included the vars file):

```bash
- name: add users
Expand All @@ -220,7 +220,7 @@ and be used inside the task like this (after having include the vars file):
loop: "{{ users }}"
```

We can use the example seen during the study of stored variables to improve it. Use of a stored variable:
We can use the example seen while studying stored variables to improve it. Use of a stored variable:

```bash
- name: /home content
Expand All @@ -235,9 +235,9 @@ We can use the example seen during the study of stored variables to improve it.

A dictionary can also be used in a loop.

In this case, you will have to transform the dictionary into an item with what is called a **jinja filter** (jinja is the templating engine used by Ansible): `| dict2items`.
In this case, you must transform the dictionary into an item with a **jinja filter** (jinja is the templating engine used by Ansible): `| dict2items`.

In the loop, it becomes possible to use `item.key` which corresponds to the dictionary key, and `item.value` which corresponds to the values of the key.
In the loop, it becomes possible to use `item.key`, which corresponds to the dictionary key, and `item.value`, which corresponds to the key's values.

Let's see this through a concrete example, showing the management of the system users:

Expand Down Expand Up @@ -267,9 +267,9 @@ Let's see this through a concrete example, showing the management of the system

!!! Note

Many things can be done with the loops. You will discover the possibilities offered by loops when your use of Ansible pushes you to use them in a more complex way.
Loops can be used for many things. When your use of Ansible pushes you to use them more complexly, you will discover the possibilities they offer.

### Exercises-2
### Exercises:

* Display the content of the `service` variable from the previous exercise using a loop.

Expand All @@ -287,11 +287,11 @@ Let's see this through a concrete example, showing the management of the system

More information can be [found here](https://docs.ansible.com/ansible/latest/user_guide/playbooks_conditionals.html).

The `when` statement is very useful in many cases: not performing certain actions on certain types of servers, if a file or a user does not exist, etc.
The `when` statement is very useful in many cases, such as not performing certain actions on certain types of servers, if a file or a user does not exist, etc.

!!! Note

Behind the `when` statement the variables do not need double braces (they are in fact Jinja2 expressions...).
Behind the `when` statement, the variables do not need double braces (they are, in fact, Jinja2 expressions...).

```bash
- name: "Reboot only Debian servers"
Expand Down Expand Up @@ -350,7 +350,7 @@ You will probably have to test that a variable exists to avoid execution errors:
when: myboolean is defined and myboolean
```

### Exercises-3
### Exercises:

* Print the value of `service.web` only when `type` equals to `web`.

Expand All @@ -360,13 +360,13 @@ when: myboolean is defined and myboolean

More information can be [found here](https://docs.ansible.com/ansible/latest/user_guide/playbooks_handlers.html).

Handlers allow to launch operations, like restarting a service, when changes occur.
When changes occur, handlers are allowed to launch operations, like restarting a service.

A module, being idempotent, a playbook can detect that there has been a significant change on a remote system, and thus trigger an operation in reaction to this change. A notification is sent at the end of a playbook task block, and the reaction operation will be triggered only once even if several tasks send the same notification.
A module, being idempotent, a playbook can detect that there has been a significant change on a remote system and thus trigger an operation in reaction to this change. A notification is sent at the end of a playbook task block, and the reaction operation will be triggered only once, even if several tasks send the same notification.

![Handlers](images/handlers.png)

For example, several tasks may indicate that the `httpd` service needs to be restarted due to a change in its configuration files. But the service will only be restarted once to avoid multiple unnecessary starts.
For example, several tasks may indicate that the `httpd` service needs to be restarted due to a change in its configuration files. However, the service will only be restarted once to avoid multiple unnecessary starts.

```bash
- name: template configuration file
Expand All @@ -380,7 +380,7 @@ For example, several tasks may indicate that the `httpd` service needs to be res

A handler is a kind of task referenced by a unique global name:

* It is activated by one or more notifiers.
* One or more notifiers activate it.
* It does not start immediately, but waits until all tasks are complete to run.

Example of handlers:
Expand Down Expand Up @@ -428,14 +428,14 @@ tasks:

More information can be [found here](https://docs.ansible.com/ansible/latest/user_guide/playbooks_async.html).

By default, SSH connections to hosts remain open during the execution of various playbook tasks on all nodes.
By default, SSH connections to hosts remain open while executing various playbook tasks on all nodes.

This can cause some problems, especially:

* if the execution time of the task is longer than the SSH connection timeout
* if the connection is interrupted during the action (server reboot for example)
* if the connection is interrupted during the action (server reboot, for example)

In this case, you will have to switch to asynchronous mode and specify a maximum execution time as well as the frequency (by default 10s) with which you will check the host status.
In this case, you will have to switch to asynchronous mode and specify a maximum execution time and the frequency (by default, 10s) with which you will check the host status.

By specifying a poll value of 0, Ansible will execute the task and continue without worrying about the result.

Expand Down Expand Up @@ -466,7 +466,7 @@ You can also decide to launch a long-running task and forget it (fire and forget

## Exercise results

* Write a playbook `play-vars.yml` that print the distribution name of the target with its major version, using global variables.
* Write a playbook, `play-vars.yml, ' using global variables, that prints the target's distribution name and major version.

```bash
---
Expand Down