Ansible - Roles

Roles provide a framework for fully independent, or interdependent collections of variables, tasks, files, templates, and modules.

In Ansible, the role is the primary mechanism for breaking a playbook into multiple files. This simplifies writing complex playbooks, and it makes them easier to reuse. The breaking of playbook allows you to logically break the playbook into reusable components.

Each role is basically limited to a particular functionality or desired output, with all the necessary steps to provide that result either within that role itself or in other roles listed as dependencies.

Roles are not playbooks. Roles are small functionality which can be independently used but have to be used within playbooks. There is no way to directly execute a role. Roles have no explicit setting for which host the role will apply to.

Top-level playbooks are the bridge holding the hosts from your inventory file to roles that should be applied to those hosts.

Creating a New Role

The directory structure for roles is essential to create a new role.

Role Structure

Roles have a structured layout on the file system. The default structure can be changed but for now let us stick to defaults.

Each role is a directory tree in itself. The role name is the directory name within the /roles directory.

$ ansible-galaxy -h 

Usage

ansible-galaxy [delete|import|info|init|install|list|login|remove|search|setup] [--help] [options] ... 

Options

• -h, --help − Show this help message and exit.
• -v, --verbose − Verbose mode (-vvv for more, -vvvv to enable connection debugging)
• --version − Show program's version number and exit.

Creating a Role Directory

The above command has created the role directories.

$ ansible-galaxy init vivekrole 
ERROR! The API server (https://galaxy.ansible.com/api/) is not responding, please try again later. 

$ ansible-galaxy init --force --offline vivekrole 
- vivekrole was created successfully 

$ tree vivekrole/ 
vivekrole/ 
├── defaults 
│   └── main.yml 
├── files ├── handlers 
│   └── main.yml 
├── meta 
│   └── main.yml 
├── README.md ├── tasks 
│   └── main.yml 
├── templates ├── tests │   ├── inventory 
│   └── test.yml 
└── vars 
    └── main.yml 
 
8 directories, 8 files

Not all the directories will be used in the example and we will show the use of some of them in the example.

Utilizing Roles in Playbook

This is the code of the playbook we have written for demo purpose. This code is of the playbook vivek_orchestrate.yml. We have defined the hosts: tomcat-node and called the two roles – install-tomcat and start-tomcat.

The problem statement is that we have a war which we need to deploy on a machine via Ansible.

--- 
- hosts: tomcat-node 
roles: 
   - {role: install-tomcat} 
   - {role: start-tomcat} 

Contents of our directory structure from where we are running the playbook.

$ ls 
ansible.cfg  hosts  roles  vivek_orchestrate.retry vivek_orchestrate.yml 

There is a tasks directory under each directory and it contains a main.yml. The main.yml contents of install-tomcat are −

--- 
#Install vivek artifacts 
-  
   block: 
      - name: Install Tomcat artifacts
         action: > 
            yum name = "demo-tomcat-1" state = present 
         register: Output 
          
   always: 
      - debug: 
         msg: 
            - "Install Tomcat artifacts task ended with message: {{Output}}" 
            - "Installed Tomcat artifacts - {{Output.changed}}" 

The contents of main.yml of the start tomcat are −

#Start Tomcat          
-  
   block: 
      - name: Start Tomcat 
      command: <path of tomcat>/bin/startup.sh" 
      register: output 
      become: true 
   
   always: 
      - debug: 
         msg: 
            - "Start Tomcat task ended with message: {{output}}" 
            - "Tomcat started - {{output.changed}}" 

The advantage of breaking the playbook into roles is that anyone who wants to use the Install tomcat feature can call the Install Tomcat role.

Breaking a Playbook into a Role

If not for the roles, the content of the main.yml of the respective role can be copied in the playbook yml file. But to have modularity, roles were created.

Any logical entity which can be reused as a reusable function, that entity can be moved to role. The example for this is shown above

Ran the command to run the playbook.

-vvv option for verbose output – verbose output 
$ cd vivek-playbook/

This is the command to run the playbook

$ sudo ansible-playbook -i hosts vivek_orchestrate.yml –vvv 
-----------------------------------------------------------------
----------------------------------------------------------------------- 

Output

The generated output is as seen on the screen −

Using /users/demo/vivek-playbook/ansible.cfg as config file.

PLAYBOOK: vivek_orchestrate.yml *********************************************************
*********************************************************** 
1 plays in vivek_orchestrate.yml 

PLAY [tomcat-node] **********************************************************************
******** ************************************************* 
 
TASK [Gathering Facts] *************************************************
****************************** ********************************************* 
Tuesday 21 November 2017  13:02:05 +0530 (0:00:00.056) 0:00:00.056 ****** 
Using module file /usr/lib/python2.7/sitepackages/ansible/modules/system/setup.py 
<localhost> ESTABLISH LOCAL CONNECTION FOR USER: root 
<localhost> EXEC /bin/sh -c 'echo ~ && sleep 0' 
<localhost> EXEC /bin/sh -c '( umask 77 && mkdir -p "` echo 
   /root/.ansible/tmp/ansible-tmp-1511249525.88-259535494116870 `" && 
   echo ansible-tmp-1511249525.88-259535494116870="` 
   echo /root/.ansible/tmp/ansibletmp-1511249525.88-259535494116870 `" ) && sleep 0' 
<localhost> PUT /tmp/tmpPEPrkd TO 
   /root/.ansible/tmp/ansible-tmp-1511249525.88259535494116870/setup.py 
<localhost> EXEC /bin/sh -c 'chmod u+x 
   /root/.ansible/tmp/ansible-tmp1511249525.88-259535494116870/ 
   /root/.ansible/tmp/ansible-tmp-1511249525.88259535494116870/setup.py && sleep 0' 
<localhost> EXEC /bin/sh -c '/usr/bin/python 
   /root/.ansible/tmp/ansible-tmp1511249525.88-259535494116870/setup.py; rm -rf 
   "/root/.ansible/tmp/ansible-tmp1511249525.88-259535494116870/" > /dev/null 2>&1 && sleep 0' 
ok: [server1] 
META: ran handlers 
 
TASK [install-tomcat : Install Tomcat artifacts] ***********************************
*************************************************************** 
task path: /users/demo/vivek-playbook/roles/install-tomcat/tasks/main.yml:5 
Tuesday 21 November 2017  13:02:07 +0530 (0:00:01.515)       0:00:01.572 ****** 
Using module file /usr/lib/python2.7/sitepackages/ansible/modules/packaging/os/yum.py 
<localhost> ESTABLISH LOCAL CONNECTION FOR USER: root 
<localhost> EXEC /bin/sh -c 'echo ~ && sleep 0' 
<localhost> EXEC /bin/sh -c '( umask 77 && mkdir -p "` echo 
   /root/.ansible/tmp/ansible-tmp-1511249527.34-40247177825302 `" && echo 
   ansibletmp-1511249527.34-40247177825302="` echo 
   /root/.ansible/tmp/ansible-tmp1511249527.34-40247177825302 `" ) && sleep 0' 
<localhost> PUT /tmp/tmpu83chg TO 
   /root/.ansible/tmp/ansible-tmp-1511249527.3440247177825302/yum.py 
<localhost> EXEC /bin/sh -c 'chmod u+x 
   /root/.ansible/tmp/ansible-tmp1511249527.34-40247177825302/ 
   /root/.ansible/tmp/ansible-tmp-1511249527.3440247177825302/yum.py && sleep 0' 
<localhost> EXEC /bin/sh -c '/usr/bin/python 
   /root/.ansible/tmp/ansible-tmp1511249527.34-40247177825302/yum.py; rm -rf 
   "/root/.ansible/tmp/ansible-tmp1511249527.34-40247177825302/" > /dev/null 2>
   &1 && sleep 0' 
changed: [server1] => { 
   "changed": true, 
   "invocation": { 
      "module_args": { 
         "conf_file": null, 
         "disable_gpg_check": false, 
         "disablerepo": null, 
         "enablerepo": null, 
         "exclude": null, 
         "install_repoquery": true, 
         "installroot": "/", 
         "list": null, 
         "name": ["demo-tomcat-1"], 
         "skip_broken": false, 
         "state": "present", 
         "update_cache": false, 
         "validate_certs": true 
      } 
   }, 
   "msg": "", 
   "rc": 0, 
   "results": [ 
      "Loaded plugins: product-id, 
      search-disabled-repos, 
      subscriptionmanager\nThis system is not registered to Red Hat Subscription Management. 
      You can use subscription-manager to register.\nResolving Dependencies\n--> 
      Running transaction check\n---> 
      Package demo-tomcat-1.noarch 0:SNAPSHOT-1 will be installed\n--> Finished Dependency 
      Resolution\n\nDependencies Resolved\n
      \n================================================================================\n 
      Package Arch Version Repository         
      Size\n==================================================================\nInstalling:\n 
      demo-tomcat-1 noarch SNAPSHOT-1 demo-repo1 7.1 M\n\nTransaction 
      Summary\n==================================================================\nInstall  1 
      Package\n\nTotal download size: 7.1 M\nInstalled size: 7.9 M\nDownloading 
         packages:\nRunning transaction 
      check\nRunning transaction test\nTransaction test succeeded\nRunning transaction\n  Installing : 
      demotomcat-1-SNAPSHOT-1.noarch 1/1 \n  Verifying  : 
      demo-tomcat-1-SNAPSHOT-1.noarch 1/1 \n\nInstalled:\n  
      demo-tomcat-1.noarch 0:SNAPSHOT-1 \n\nComplete!\n" 
   ] 
} 
 
TASK [install-tomcat : debug] **********************************************************
*************************************************************************** 
task path: /users/demo/vivek-playbook/roles/install-tomcat/tasks/main.yml:11 
Tuesday 21 November 2017  13:02:13 +0530 (0:00:06.757) 0:00:08.329 ****** 
ok: [server1] => { 
   "changed": false, 
   "msg": [ 
      "Install Tomcat artifacts task ended with message: {
         u'msg': u'', u'changed': True, u'results': 
         [u'Loaded plugins: product-id, 
         search-disabledrepos, 
         subscription-manager\\nThis system is not registered to Red Hat Subscription Management. 
         You can use subscription-manager to register.\\nResolving Dependencies\\n--> 
         Running transaction check\\n---> 
         Package demo-tomcat-1.noarch 0:SNAPSHOT-1 will be installed\\n--> 
         Finished Dependency Resolution\\n
         \\nDependencies 
         Resolved\\n\\n==================================================================\\n 
         Package Arch Version Repository         
         Size\\n======================================================================== 
         =====\\nInstalling:\\n demo-tomcat-1 noarch SNAPSHOT-1 demo-repo1 7.1 M\\n\\nTransaction 
         Summary\\n=========================================================\\nInstall  1 
         Package\\n\\nTotal download size: 7.1 M\\nInstalled size: 7.9 M\\nDownloading 
            packages:\\nRunning 
         transaction check\\nRunning transaction test\\nTransaction test succeeded\\nRunning 
            transaction\\n  
         Installing : demo-tomcat-1-SNAPSHOT-1.noarch 1/1 \\n  Verifying  : 
         demo-tomcat-1-SNAPSHOT-1.noarch
         1/1 \\n\\nInstalled:\\n  demo-tomcat-1.noarch 0:SNAPSHOT-1  \\n\\nComplete!\\n'], u'rc': 0
      }", 
      "Installed Tomcat artifacts - True" 
   ] 
} 
 
TASK [install-tomcat : Clean DEMO environment] ****************************************
************************************************************ 
task path: /users/demo/vivek-playbook/roles/install-tomcat/tasks/main.yml:19 
Tuesday 21 November 2017  13:02:13 +0530 (0:00:00.057) 0:00:08.387 ****** 
[WARNING]: when statements should not include jinja2 templating delimiters such as {{ }} or 
   {% %}. Found: {{installationOutput.changed}} 
 
Using module file /usr/lib/python2.7/sitepackages/ansible/modules/files/file.py 
<localhost> ESTABLISH LOCAL CONNECTION FOR USER: root 
<localhost> EXEC /bin/sh -c 'echo ~ && sleep 0' 
<localhost> EXEC /bin/sh -c '( umask 77 && mkdir -p "` echo 
   /root/.ansible/tmp/ansible-tmp-1511249534.13-128345805983963 `" && echo 
   ansible-tmp-1511249534.13-128345805983963="` echo 
   /root/.ansible/tmp/ansibletmp-1511249534.13-128345805983963 `" ) && sleep 0' 
<localhost> PUT /tmp/tmp0aXel7 TO 
   /root/.ansible/tmp/ansible-tmp-1511249534.13128345805983963/file.py 
<localhost> EXEC /bin/sh -c 'chmod u+x 
   /root/.ansible/tmp/ansible-tmp1511249534.13-128345805983963/ 
   /root/.ansible/tmp/ansible-tmp-1511249534.13128345805983963/file.py && sleep 0' 
<localhost> EXEC /bin/sh -c '/usr/bin/python 
   /root/.ansible/tmp/ansible-tmp1511249534.13-128345805983963/file.py; rm -rf 
   "/root/.ansible/tmp/ansible-tmp1511249534.13-128345805983963/" > /dev/null 2>&1 
   && sleep 0' 
changed: [server1] => { 
   "changed": true, 
      "diff": { 
         "after": { 
            "path": "/users/demo/DEMO", 
            "state": "absent" 
      }, 
      "before": { 
         "path": "/users/demo/DEMO", 
         "state": "directory" 
      } 
   },

   "invocation": { 
      "module_args": { 
         "attributes": null, 
         "backup": null, 
         "content": null, 
         "delimiter": null, 
         "diff_peek": null, 
         "directory_mode": null, 
         "follow": false, 
         "force": false, 
         "group": null, 
         "mode": null, 
         "original_basename": null, 
         "owner": null, 
         "path": "/users/demo/DEMO", 
         "recurse": false, 
         "regexp": null, 
         "remote_src": null, 
         "selevel": null, 
         "serole": null, 
         "setype": null, 
         "seuser": null, 
         "src": null, 
         "state": "absent", 
         "unsafe_writes": null, 
         "validate": null 
      } 
   }, 
   "path": "/users/demo/DEMO", 
   "state": "absent" 
} 
 
TASK [install-tomcat : debug] ********************************************************
************************************************************* 
task path: /users/demo/vivek-playbook/roles/install-tomcat/tasks/main.yml:29 
Tuesday 21 November 2017  13:02:14 +0530 (0:00:00.257)       0:00:08.645 ****** 
ok: [server1] => {
   "changed": false, 
   "msg": [ 
      "Clean DEMO environment task ended with message:{u'diff': {u'after': {u'path': 
         u'/users/demo/DEMO', u'state': u'absent'}, 
      u'before': {u'path': u'/users/demo/DEMO', u'state': u'directory'}}, u'state': u'absent', 
         u'changed': True, u'path': u'/users/demo/DEMO'}", 
      "check value  :True" 
   ] 
} 
 
TASK [install-tomcat : Copy Tomcat to user home] *************************************
******************************************************** 
task path: /users/demo/vivek-playbook/roles/install-tomcat/tasks/main.yml:37 
Tuesday 21 November 2017  13:02:14 +0530 (0:00:00.055)       0:00:08.701 ****** 
[WARNING]: when statements should not include jinja2 templating delimiters such as {{ }} or 
   {% %}. Found: {{installationOutput.changed}} 
 
Using module file /usr/lib/python2.7/sitepackages/ansible/modules/commands/command.py 
<localhost> ESTABLISH LOCAL CONNECTION FOR USER: root 
<localhost> EXEC /bin/sh -c 'echo ~ && sleep 0' 
<localhost> EXEC /bin/sh -c '( umask 77 && mkdir -p "` echo 
   /root/.ansible/tmp/ansible-tmp-1511249534.43-41077200718443 `" && echo 
   ansibletmp-1511249534.43-41077200718443="` echo 
   /root/.ansible/tmp/ansible-tmp1511249534.43-41077200718443 `" ) && sleep 0' 
<localhost> PUT /tmp/tmp25deWs TO 
   /root/.ansible/tmp/ansible-tmp-1511249534.4341077200718443/command.py 
<localhost> EXEC /bin/sh -c 'chmod u+x 
   /root/.ansible/tmp/ansible-tmp1511249534.43-41077200718443/ 
   /root/.ansible/tmp/ansible-tmp-1511249534.4341077200718443/command.py && sleep 0' 
<localhost> EXEC /bin/sh -c '/usr/bin/python 
   /root/.ansible/tmp/ansible-tmp1511249534.43-41077200718443/command.py; rm -rf 
   "/root/.ansible/tmp/ansibletmp-1511249534.43-41077200718443/" > /dev/null 2>&1 
   && sleep 0' 
changed: [server1] => { 
   "changed": true, 
   "cmd": [ 
      "cp", 
      "-r", 
      "/opt/ansible/tomcat/demo", 
      "/users/demo/DEMO/" 
   ],
   "delta": "0:00:00.017923", 
   "end": "2017-11-21 13:02:14.547633", 
   "invocation": { 
      "module_args": { 
         "_raw_params": "cp -r /opt/ansible/tomcat/demo /users/demo/DEMO/", 
         "_uses_shell": false, 
         "chdir": null, 
         "creates": null, 
         "executable": null, 
         "removes": null, 
         "warn": true 
      } 
   }, 
   "rc": 0, 
   "start": "2017-11-21 13:02:14.529710", 
   "stderr": "", 
   "stderr_lines": [], 
   "stdout": "", 
   "stdout_lines": [] 
} 
 
TASK [install-tomcat : debug] ********************************************************
********************************************************** 
task path: /users/demo/vivek-playbook/roles/install-tomcat/tasks/main.yml:47 
Tuesday 21 November 2017  13:02:14 +0530 (0:00:00.260)       0:00:08.961 ****** 
ok: [server1] => { 
   "changed": false, 
   "msg": "Copy Tomcat to user home task ended with message {
      'stderr_lines': [], u'changed': True, u'end': u'2017-11-21 13:02:14.547633', u'stdout': 
      u'', u'cmd': [u'cp', u'-r', u'/opt/ansible/tomcat/demo', u'/users/demo/DEMO/'], u'rc': 0, 
      u'start': u'2017-11-21 13:02:14.529710', u'stderr': u'', u'delta': u'0:00:00.017923', 
      'stdout_lines': []}" 
} 
 
TASK [start-tomcat : Start Tomcat] **************************************************
********************************************************** 
task path: /users/demo/vivek-playbook/roles/start-tomcat/tasks/main.yml:5 
Tuesday 21 November 2017  13:02:14 +0530 (0:00:00.044)       0:00:09.006 ****** 
Using module file /usr/lib/python2.7/sitepackages/ansible/modules/commands/command.py 
<localhost> ESTABLISH LOCAL CONNECTION FOR USER: root 
<localhost> EXEC /bin/sh -c 'echo ~ && sleep 0' 
<localhost> EXEC /bin/sh -c '( umask 77 && mkdir -p "` echo 
   /root/.ansible/tmp/ansible-tmp-1511249534.63-46501211251197 `" && echo 
   ansibletmp-1511249534.63-46501211251197="` echo 
   /root/.ansible/tmp/ansible-tmp1511249534.63-46501211251197 `" ) && sleep 0' 
<localhost> PUT /tmp/tmp9f06MQ TO 
   /root/.ansible/tmp/ansible-tmp-1511249534.6346501211251197/command.py 
<localhost> EXEC /bin/sh -c 'chmod u+x 
   /root/.ansible/tmp/ansible-tmp1511249534.63-46501211251197/ 
   /root/.ansible/tmp/ansible-tmp-1511249534.6346501211251197/command.py && sleep 0' 
<localhost> EXEC /bin/sh -c '/usr/bin/python 
   /root/.ansible/tmp/ansible-tmp1511249534.63-46501211251197/command.py; rm -rf 
   "/root/.ansible/tmp/ansibletmp-1511249534.63-46501211251197/" > /dev/null 2>&1 
   && sleep 0' 
changed: [server1] => { 
   "changed": true, 
   "cmd": [ "/users/demo/DEMO/bin/startup.sh" ], 
   "delta": "0:00:00.020024", 
   "end": "2017-11-21 13:02:14.741649", 
   "invocation": { 
      "module_args": { 
         "_raw_params": "/users/demo/DEMO/bin/startup.sh", 
         "_uses_shell": false, 
         "chdir": null, 
         "creates": null, 
         "executable": null, 
         "removes": null, 
         "warn": true 
      } 
   }, 
   "rc": 0, 
   "start": "2017-11-21 13:02:14.721625", 
   "stderr": "", 
   "stderr_lines": [], 
   "stdout": "Tomcat started.", 
   "stdout_lines": [ "Tomcat started." ] 
} 
 
TASK [start-tomcat : debug] *************************************************
********************************************************************** 
task path: /users/demo/vivek-playbook/roles/start-tomcat/tasks/main.yml:10 
Tuesday 21 November 2017  13:02:14 +0530 (0:00:00.150)       0:00:09.156 ****** 
ok: [server1] => { 
   "changed": false, 
   "msg": [ 
      "Start Tomcat task ended with message: {'
         stderr_lines': [], u'changed': True, u'end': u'2017-11-21 13:02:14.741649', u'stdout': 
         u'Tomcat started.', u'cmd': [u'/users/demo/DEMO/bin/startup.sh'], u'rc': 0, u'start': 
         u'2017-11-21 13:02:14.721625', u'stderr': u'', u'delta': u'0:00:00.020024', 
         'stdout_lines': [u'Tomcat started.']}", 
      "Tomcat started - True" 
   ] 
} 
META: ran handlers 
META: ran handlers 
 
PLAY RECAP ******************************************************************************* 
********************************************************* 
server1  : ok = 9    changed = 4    unreachable = 0    failed = 0 
 
Tuesday 21 November 2017  13:02:14 +0530 (0:00:00.042)       0:00:09.198 ****** 
=============================================================================== 
install-tomcat : Install Tomcat artifacts ------------------------------- 6.76s 
/users/demo/vivek-playbook/roles/install-tomcat/tasks/main.yml:5 -------------- 
Gathering Facts --------------------------------------------------------- 1.52s 
 ------------------------------------------------------------------------------ 
install-tomcat : Copy Tomcat to user home ------------------------------- 0.26s 
/users/demo/vivek-playbook/roles/install-tomcat/tasks/main.yml:37 ------------- 

install-tomcat : Clean DEMO environment --------------------------------- 0.26s 
/users/demo/vivek-playbook/roles/install-tomcat/tasks/main.yml:19 ------------- 

start-tomcat : Start Tomcat --------------------------------------------- 0.15s 
/users/demo/vivek-playbook/roles/start-tomcat/tasks/main.yml:5 ----------------

install-tomcat : debug -------------------------------------------------- 0.06s 
/users/demo/vivek-playbook/roles/install-tomcat/tasks/main.yml:11 ------------- 

install-tomcat : debug -------------------------------------------------- 0.06s 
/users/demo/vivek-playbook/roles/install-tomcat/tasks/main.yml:29 ------------- 

install-tomcat : debug -------------------------------------------------- 0.04s 
/users/demo/vivek-playbook/roles/install-tomcat/tasks/main.yml:47 ------------- 

start-tomcat : debug ---------------------------------------------------- 0.04s 
/users/demo/vivek-playbook/roles/start-tomcat/tasks/main.yml:10 --------------- 

Hit the following URL and you will be directed to a page as shown below − http://10.76.0.134:11677/HelloWorld/HelloWorld

The deployed war just has a servlet which displays “Hello World”. The detailed output shows the time taken by each and every task because of the entry added in ansible.cfg file −

[defaults] 
callback_whitelist = profile_tasks 

Getting started writing your first playbook

What is a Playbook?

Playbooks are essentially sets of instructions (plays) that you send to run on a single target or groups of targets (hosts). Think about the instructions you get for assembling an appliance or furniture. The manufacturer includes instructions so you can put the parts together in the correct order. When followed in order, the furniture looks like what was purchased.

That's basically how a playbook works.

Modules

The Playbook we're building will install a web server on a target RHEL/CentOS 7 host, then write an index.html file based on a template file that will reside with the final Playbook. You'll be able to take the example Playbook and additional files from this blog and test it out for yourself. While going over the example Playbook, we'll explain the modules that are used.

Authors

The author adds instructions for the modules to run, often with additional values (arguments, locations, etc.). The target host has modules run against it in the order the Playbook lays out (with includes or other additional files). The host's state is changed (or not) based on the results of the module running, which Ansible and Tower displays in output.

Running Playbooks

Keeping that in mind, you're still going to need to understand a few things about running Playbooks. With the furniture analogy, a Playbook is shorthand to tell the modules to perform a task. You must understand the following to run your Playbook successfully:

1. The target

Because the Playbooks are providing direction and interactivity with the modules, Ansible assumes you know how to do what you're trying to do and automates it. That's why Playbooks are like instructions or directions - you're telling the automated parts how you want the task configured. You'll still need to understand the target you're running the Playbook against.

2. The tasks

If part of the Playbook needs to start the web server, you're going to need to know how that's done so you know to use the service module and start the web server by name. If the Playbook is installing software, then you have to know how installation is done on the target. You're also still going to need to understand the basics of the tasks being performed. Does the software you're installing have a configuration setup to it? Are there multiple steps that require conditions or argument values? If there are variables that are being passed, these will all need to be understood by those constructing a Playbook as well.

Example Playbook

We'll share an example Playbook with a simple play to demonstrate what I've explained. The target host will be a RHEL/CentOS 7 base install. There will be a web server installed (NGINX) and then an index.html file will be created in the default webroot. After the install and file tasks are completed the service will be started.
*Note to run this example Playbook with Ansible Tower your inventory and credentials must be configured. 

Playbooks start with the YAML three dashes (---) followed by:

Name: good for keeping the Playbooks readable

Hosts: identifies the target for Ansible to run against

Become statements: true statement is included here to ensure nginx installs without a problem (it's not always required)

---
- name: Install nginx
  hosts: host.name.ip
  become: true

On the same indent level as the three prior statements will go the tasks: statement, after which any plays are listed another indent deeper (per YAML nesting). There are two tasks listed but both are using the Yum module. The first Yum task is adding the epel-release repo so that nginx can be installed. Once epel is present Yum is used to install the nginx package.

The state: present statement lets Ansible check the state on the target first before performing any further action. In both cases if the repo or package is already present, Ansible knows it doesn't have to do any more for this task and continues.

tasks:
  - name: Add epel-release repo
    yum:
      name: epel-release
      state: present

  - name: Install nginx
    yum:
      name: nginx
      state: present

The default install page for nginx is fine if you want to test that nginx installed properly, but you might have a basic html file that you'd like to have as your confirmation. For simplicity, the template index file is in the same directory I'll run the Playbook from for the example. The destination is simply the default for nginix with no configured sites.

  - name: Insert Index Page
    template:
      src: index.html
      dest: /usr/share/nginx/html/index.html

The last thing the Playbook will do is make sure that the nginx service has been started (and if not, start it).

- name: Start NGiNX
    service:
      name: nginx
      state: started

The entire Playbook is about the same length as the introduction paragraph:

---
- name: Install nginx
  hosts: host.name.ip
  become: true

  tasks:
  - name: Add epel-release repo
    yum:
      name: epel-release
      state: present

  - name: Install nginx
    yum:
      name: nginx
      state: present

  - name: Insert Index Page
    template:
      src: index.html
      dest: /usr/share/nginx/html/index.html

  - name: Start NGiNX
    service:
      name: nginx
      state: started