Hello there! We are looking for some free identities providers and some names crossed our minds such as fusionauth, keycloak, auth0, zitadel, etc.

Currently we use WSO2 with a very outdated version and we have had a huge headache trying to update it in the recent past. Even with the paid help from the WSO2 team, it failed.

The most important requirement is to perform well with a load of millions of users. We currently have around 7K tenants and over 8.5M users (although monthly active is about 600k). At peak hours it reaches 1.8~2K login requests per minute.

We use AWS, so we tested fusionauth as a deployment on Amazon EKS and an RDS instance with postgres. We haven't tested ElasticSearch as a search engine though. Scaling it horizontally and setting higher JVM memory under the fusionauth-app.memory environment variable managed to handled the 7k tenants and 10.5 millions users in database with loads of 50 requests per second (3k per minute).

That said, what concerns us most is the limitation we found here: https://fusionauth.io/docs/v1/tech/reference/limitations#system-upgrade-downtime (open issue: https://github.com/FusionAuth/fusionauth-issues/issues/1240).

If I understand correctly, every time the database needs to be migrated it will cost us some donwtime. If yes, is there a prediction to solve it to be possible doing the migration with zero downtime? For us, donwtime is 100% out of the question, even for a very short period of time. And we don't want to fall into the same trap that was with WSO2, freezing its version and being very outdated.

Thanks!