Election Algorithms

Many distributed algorithms need one process to act as a leader or coordinator. It doesn’t matter which process does the job, just need to pick one.

Coordinate the actions performed by a collection of collaborating instances in a distributed application by electing one instance as the leader that assumes responsibility for managing the others. This can help to ensure that instances don't conflict with each other, cause contention for shared resources, or inadvertently interfere with the work that other instances are performing.

 

Solution

A single task instance should be elected to act as the leader, and this instance should coordinate the actions of the other subordinate task instances. If all of the task instances are running the same code, they are each capable of acting as the leader. Therefore, the election process must be managed carefully to prevent two or more instances taking over the leader role at the same time.

The system must provide a robust mechanism for selecting the leader. This method has to cope with events such as network outages or process failures. In many solutions, the subordinate task instances monitor the leader through some type of heartbeat method, or by polling. If the designated leader terminates unexpectedly, or a network failure makes the leader unavailable to the subordinate task instances, it's necessary for them to elect a new leader.

There are several strategies for electing a leader among a set of tasks in a distributed environment, including:

• Selecting the task instance with the lowest-ranked instance or process ID.


• Racing to acquire a shared, distributed mutex. The first task instance that acquires the mutex is the leader. However, the system must ensure that, if the leader terminates or becomes disconnected from the rest of the system, the mutex is released to allow another task instance to become the leader.


• Implementing one of the common leader election algorithms such as the Bully Algorithm or the Ring Algorithm. These algorithms assume that each candidate in the election has a unique ID, and that it can communicate with the other candidates reliably.

MORE DETAILS ON THE LINKS BELOW;

 

Ch6-Election

Distributed Algorithms