Problem
Terraform Enterprise (TFE) >= v202406-1 fails to start due to the following Redis error:
Health check Failure (redis) : ERR DB index is out of range
Background
This is due to the TFE dependency on Sidekiq, and a change made in v202406-1 to allow upgrading to a later version of Sidekiq. This update requires an additional Redis database to be used and so causes a failure for TFE installations relying on Redis server implementations without multiple database indexes (typically non-OSS Redis).
Solutions
Option 1: Migrate to a multi-database/OSS implementation of Redis server, like ElastiCache Redis OSS on AWS.
Option 2: If using Redis Enterprise, upgrade to TFE version v202411-1 or later and configure the Redis Enterprise application settings.
Option 3: If using Redis Sentinel, upgrade to TFE version v202503-1 or later and configure the Redis Sentinel application settings.