How can I upgrade Graylog 4.0 to Graylog 7.0?
You would have to upgrade to through each version (4.0>4.1>4.2), starting up graylog after each upgrade.
It should theoretically work from 4 to 7, there weren’t any earth shattering changes, however if a customer asked for it our PS team would probably recommend starting over in most cases as its often less risky.
If you do decide to run the upgrade path, make sure you reference this compatibility matrix at each step. Also pay attention to updating Elastic/Opensearch as there are Lucene incompatibilities between versions.
Same goes for MongoDB, depending on which version you are coming from there will be a correct upgrade path to step through.