Difference between Fork and Serial in Ansible

Ansible is a popular open-source automation tool that is used to manage and configure servers, network devices, and other IT infrastructure. One of the key features of Ansible is its ability to run tasks in parallel or serially, depending on the requirements of the task. In this tutorial, we will discuss the difference between fork and serial in Ansible and how they can be used to manage infrastructure.

S.No.	Fork	Serial
1	Run multiple tasks in parallel on multiple hosts	Run tasks in sequence on a single host
2	Perform a task on a large number of hosts quickly	Perform a task on a single host in a specific order or on multiple hosts one at a time
3	Updating software on 100 servers simultaneously	Updating software on 100 servers in a specific order one at a time

1. Fork

The “fork” option in Ansible is used to run multiple tasks in parallel on multiple hosts. This is useful when you need to perform a task on a large number of hosts quickly, as it allows you to take advantage of the processing power of multiple hosts at the same time. For example, if you need to update the software on 100 servers, you can use the “fork” option to update all of the servers at the same time, rather than having to update them one at a time.

2. Serial

The “serial” option in Ansible is used to run tasks in sequence on a single host. This is useful when you need to perform a task on a single host in a specific order, or when you need to perform a task on multiple hosts one at a time. For example, if you need to update the software on 100 servers, but you need to update them in a specific order, you can use the “serial” option to update the servers one at a time.

Configure Fork in Ansible:

The number of forks can be specified in the Ansible configuration file (ansible.cfg) or on the command line when running the ansible-playbook command. The default value for forks is 5, but this can be increased or decreased depending on the number of hosts and resources available.

For example, to set the number of forks to 10, you can add the following line to the ansible.cfg file:

forks = 10

or you can use the -f option when running the ansible-playbook command:

ansible-playbook -f 10 myplaybook.yml

In addition to setting the number of forks in the Ansible configuration file or on the command line, you can also set the number of forks at the task or play level in a playbook.

For example, to set the number of forks for a specific task, you can use the async and poll options in the task definition. The async option specifies the number of forks for the task, and the poll option specifies the interval at which Ansible will check for the completion of the task.

- name: My task
  command: /usr/bin/mycommand
  async: 10
  poll: 10

Configure Serial in Ansible:

You can set the number of hosts that are executed in a single batch using the serial keyword in the play definition.

- name: My Play
  hosts: all
  serial: 5
  tasks:
   - name: My task 1
     command: /usr/bin/mycommand1
   - name: My task 2
     command: /usr/bin/mycommand2

In this example, only 5 hosts will be executed at a time, so if you have 20 hosts, it will take 4 batches to complete the play.

In conclusion, the “fork” and “serial” options in Ansible are useful tools for managing your infrastructure, depending on the requirements of your tasks. The “fork” option is useful for running tasks in parallel on multiple hosts, while the “serial” option is useful for running tasks in sequence on a single host. Understanding when to use these options can help you to manage your infrastructure more efficiently and effectively.

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