The Guardian’s Migration From MongoDB to PostgreSQL on Amazon RDS
The Guardian migrated their CMS’s datastore in 2018 from a self-managed MongoDB cluster to PostgreSQL on Amazon RDS for a fully managed solution. The team did an API-based migration without any downtime. Guardian’s in-house CMS – called Composer – which stores articles, blog content, photo galleries and video was originally built on top of MongoDB as a datastore.
This was preceded by a vendor software backed by an Oracle database. This setup had downtimes whenever the schema had to be migrated. As an alternative, the team looked at various NoSQL dbs, and one of the key reasons for choosing MongoDB seems to have been flexibility.
Originally hosted on their own datacenter, they moved their MongoDB to their AWS servers after an outage. The installation and management scripts had to be handwritten by Guardian’s team. They opted for a support contract and bought the OpsManager tool, which is a frontend application for managing MongoDB.
However, the team did not go for MongoDB’s Atlas offering, which is a ‘fully managed database’, for reasons which are unclear. OpsManager does not manage deployments. After moving to AWS, the team faced two MongoDB outages.
Some of them the reasons were basic system administration issues, like not allowing NTP to access time servers to keep clocks in sync. Others pertained to the difficulty of managing OpsManager itself and obtaining timely support from the vendor, according to the article. The team felt that moving to a solution which had minimal database management would suit them best.