Problem
Terraform Enterprise (TFE) version v202406-1 or newer fails to start and displays the following Redis error.
Health check Failure (redis) : ERR DB index is out of range
Cause
This issue occurs because of a change in TFE v202406-1 that updated its Sidekiq dependency. This update requires an additional Redis database index that is not available in certain Redis server implementations, such as some non-OSS versions of Redis.
As a result, TFE installations that rely on a Redis server without support for multiple database indexes will fail to start.
Solutions
There are three potential solutions depending on your Redis implementation and ability to upgrade Terraform Enterprise.
Solution 1: Migrate to a Multi-Database Redis Implementation
Migrate your Redis data store to an open-source software (OSS) or multi-database compatible implementation. An example of a compatible service is ElastiCache for Redis on AWS.
Solution 2: Upgrade TFE for Redis Enterprise Support
If you are using Redis Enterprise, upgrade to Terraform Enterprise version v202411-1 or later. This version and subsequent releases include updated application settings to support Redis Enterprise.
Solution 3: Upgrade TFE for Redis Sentinel Support
If you are using Redis Sentinel, upgrade to Terraform Enterprise version v202503-1 or later. This version and subsequent releases include updated application settings to support Redis Sentinel.