Introduction

Concept

In contrast to regular nodes (inactive -> active), lifecycle nodes transition through 4 primary states:

• unconfigured
  • action: configure
• inactive
  • action: activate
• active
• finalised
  This is described in the following diagram:
  

Use-Case

Nav2 navigation stack uses lifecycle nodes to manage transitions and ensure that the stack can successfully execute without missing any nodes.

It configures and activates nodes in a particular sequence to start up the stack, then goes in reverse order to bring it back down into a finalised state.

Whenever a single node fails to transition to configured state, other nodes are also blocked from becoming active. It also transitions down all nodes if any connected planning servers are non-responsive or have crashed.

• This is critical because controller-server is in charge of local obstacle avoidance.
• If it fails its activation and isn't running correctly, the other navigation nodes should not start, as robot could collide into obstacles while executing its tasks.