Implementing Process Locks in vRO Workflows

I discovered last week that a developer wasn’t aware that you could use a locking semaphore in vRO. They were writing some API calls and encountered a 409 (conflict) error when a workflow was attempting to concurrently update the same resource (a load balancer if I recall but can’t remember the exact details). I felt that there may be other developers out there who are also not aware so I have created two workflows that can be used to create and remove process locks in your vRO workflows.

vRO provides an always available Locking System that can be used to create a lock for a given id and owner. It does this by creating a record in the embedded PostgreSQL database. When an attempt is made to create another record in the database, a key constraint occurs and the lock fails.

You should consider using a process lock if you are updating any resources that could cause a conflict or data consistency problems. Some examples include, updating a load balancer, updating a vRA Reservation, or preventing a data collection task from running because there is already one in progress. It is also useful to create a lock between sections of code in your workflow, which could cause a problem if the workflow was executed multiple times, simultaneously. Note, that you don’t always need to lock the entire workflow, just between areas of code where updates are performed. Continue reading