Introduction
Camunda has, in my opinion, one of the best capacities for process instance migrations in any platform. But don’t let that fool you. Just because Camunda is good at migration, that doesn’t mean it’s an easy thing to do! Today, we’ll talk about five things you need to consider as you migrate instances from one version of Camunda to another, with a special section just for migrating from Camunda 7 to 8.
Data consistency
You need to ensure that all of the data associated with the process instance being migrated is consistent and up-to-date. This includes tasks, variables, and any other data that is relevant to the process.
Consistency is critical when performing process instance migration in Camunda. It can act as sanity check for your before/after migration, and is often the best metric.
One way to ensure data consistency is to perform a thorough review of the data before the migration takes place. This can include:
- Checking for any inconsistencies or errors in the data.
- Making any necessary corrections.
You may also want to consider running tests to ensure that the data is being migrated correctly.
It is also important to consider how the data will be used in the target process definition. For example, if the data types of the variables in the original process definition do not match the data types in the target process definition, you will need to address this issue before the migration can take place.
Ensuring data consistency is critical for the success of the process instance migration, as it will help ensure that the migrated process runs smoothly and effectively.
Target process definition
You need to consider the target process definition that you will be migrating the process instance to. This includes ensuring that the target process definition has the same data variables and data types as the original process definition.
Start by reviewing the data variables and data types in both the original and target process definitions to ensure that they are compatible. Take times, events, and transactions into account. This may involve making changes to either the original or target process definition to ensure that the data can be migrated correctly.
It is also important to consider how the data will be used in the target process definition. For example, if the data types of the variables in the original process definition do not match the data types in the target process definition, or, for example, you’re not using the data consistently, you’re going to have a bad time.
Ensuring that the target process definition is compatible with the data in the original process definition is key for the success of the process instance migration, if you want the migrated process to run smoothly and effectively in their new home(s).
Mapping of process variables
You will need to map the process variables from the original process definition to the target process definition. This includes ensuring that the data types match and that any custom variables are handled correctly. It also involves matching the variables in the original process definition to the corresponding variables in the target process definition.
I find it best to start by creating a mapping table that lists the variables in the original process definition and their corresponding variables in the target process definition. This can help ensure that all of the variables are correctly mapped, and that any custom variables are handled correctly.
It is important to ensure that the data types of the variables in the original process definition match the data types in the target process definition. If the data types do not match, you may need to make changes to either the original or target process definition to ensure that the data can be migrated correctly.
Mapping process variables is a critical step in the process instance migration process, as it helps ensure that the migrated process runs smoothly and effectively.
Process instance state
You need to consider the state of the process instance being migrated. If the process instance is currently executing a task, you will need to ensure that the task is completed or otherwise handled before the migration can take place.
If the process instance is done executing a task, you will need to ensure that the task is completed or otherwise handled before the migration can take place.
One way to handle this is to use a process engine API to complete the task before the migration takes place. This will allow you to migrate the process instance without having to worry about any tasks being left in an incomplete state.
For example, something like this.
It is also important to consider any dependencies that the process instance may have on other process instances or external systems. For example, if the process instance is waiting for a response from an external system, you will need to ensure that this response has been received before the migration can take place.
Ensuring that the process instance is in a stable state before migration will help ensure that the migrated process runs smoothly and effectively.
Rollback capabilities
You should consider whether or not you need to have the ability to roll back the migration if something goes wrong. This could include having a backup of the original process definition or being able to revert to an earlier version of the process instance.
One way to provide rollback capabilities is to keep a backup of the original process definition, so that it can be used to revert the migration if necessary. This can be especially useful if you are making significant changes to the process definition as part of the migration.
Another option is to use version control for the process definition, which would allow you to revert to an earlier version of the process if necessary. This could be especially useful if you are making incremental changes to the process definition over time, as it would allow you to easily roll back to a previous version if needed.
Rollback capabilities can be an important safety net in the process instance migration process, as they can help ensure that you are able to recover from any issues that may arise during or after the migration.
Migration from Camunda 7 to 8
Migrating process instances from Camunda 7 to Camunda 8 involves creating a migration plan for each process instance and then executing the migration plan using the Camunda Engine API.
A migration plan specifies how a process instance should be migrated from one process definition to another. It defines the mapping between the activities in the source process definition and the activities in the target process definition. You can use the Camunda Engine API to create a migration plan and then use it to migrate a process instance.
Here is an example of how you can create a migration plan using the Camunda Engine API:
This creates a migration plan that maps equal activities between the source and target process definitions. You can also specify more complex mappings if necessary.
Once you have created the migration plan, you can use it to migrate a process instance like this:
So, you might have something like this:
This code uses the RepositoryService and RuntimeService to get the process definition and process instance you want to migrate. It then creates a migration plan using the RuntimeService, specifying the mapping between the activities in the source process definition and the target process definition. Finally, it executes the migration plan using the RuntimeService, passing in the ID of the process instance to be migrated.
The mapEqualActivities method specifies that activities with the same ID in the source and target process definitions should be mapped to each other. You can, and should, specify more complex mappings as necessary.