8. Tasks¶

Before we can start with Tasks, we need to know YAML.

8.1. YAML is your friend¶

yaml stores structured data as text
Ansible uses YAML because it’s easy to read and write
nearly every YAML file starts with a list
an item in the list is a list of key / value pairs
the key / value pairs are commonly called hash or dictionary
a YAML file begins with ---
YAML cares about whitespaces and refuses tab character
the amount of whitespaces is free, often are 2 whitespaces used

8.1.1. String / Numeric value¶

string values don’t need quotes, but recommended (to avoid spaces)
simple key/value pairs

username: 'foo'
gid: 55

8.1.2. List¶

ordered sequence
can be nested
all members of a list begins with - (dash and space)

# a list named userlist with two items
userlist:
  - foo
  - bar

8.1.3. Dictionary¶

a dictionary is represented in a key: value form (space is needed)
unordered group of key/value pairs
indentation is needed
can be nested

# a dictionary named user with two key/values (string)
user:
  username: foo
  home: /home/foo

8.1.4. Nested¶

more complicated data structures are possible
dictionaries and lists can be nested
indentation is used for nesting
example
- a list with 2 items
- dictionaries whose values are lists
- a mix of both

---
- pascal:                        <- 1st list item with a dictionary item
    name: Pascal Stauffer        <- key / value pair
    series:                      <- list with 3 items (indentation!)
      - suits
      - house of cards
      - dexter
- domi:                          <- 2nd list item with a dictionary item
    name: Domi Barton            <- key / value pair
    series:                      <- list with 3 items (indentation!)
      - breaking bad
      - happy endings
      - last man on earth

# dict.name / dict['name'] = string
# dict.series / dict['series'] = list

Hint

A list always containts a dash -, so you can differate between a list and a dictionary.

Dictionaries and lists can also be represented in a short form

# dictionary short form
martin: {name: Martin D'vloper, job: Developer, skill: Elite}

# list short form
fruits: ['Apple', 'Orange', 'Strawberry', 'Mango']

Hint

Don’t use the short form. It can be difficult to read and is hard to compare with a SCM tool.

8.1.5. Multiple lines¶

values can span multiple lines using | or >
| will include the newlines
> will ignore newlines

include_newlines: |
            exactly as you see
            will appear these three
            lines of poetry

ignore_newlines: >
            this is really a
            single line of text
            despite appearances

8.1.6. Links¶

http://docs.ansible.com/ansible/YAMLSyntax.html

8.2. What’s a Task¶

a task defines a state
tasks are written in YAML syntax
calls a module with parameters
tasks are executed in order
tasks can be written on one or more lines
tasks run parallel on servers (default 5)
order of the hosts depends on the response time
the next task will started, if it run on every server
if a task fails, the following tasks will be skipped on this server

# recommended form
- name: install httpd package    <- documentation
  yum:                           <- module
    name: httpd                  <- arguments
    state: present

# short form
- apt: name=apache2 state=present

Hint

Don’t use the short form. With a lots of arguments, the line will be too long. And it’s difficutlt to compare with a SCM tool.

8.2.1. Run a ad-hoc task/command¶

a task can be run with the ansible binary.

ansible -m apt -a "name=apache2 state=latest" web1.pascal.lab