You set MONGO_INITDB_ROOT_USERNAME and MONGO_INITDB_ROOT_PASSWORD in Compose, start the official mongo image, and your app logs MongoServerError: Authentication failed. The password is right. You can see it in the container's environment. Or you changed the password in .env , recreated the container, and now nothing can log in. Or the user your docker-entrypoint-initdb.d script should create never shows up.

This guide reproduces each of those failures with mongo:9.0.4 in Docker Compose and fixes them. Every error and log line below comes from that lab run on November 1, 2026, when mongo:latest pointed to the same 9.0.4 image digest. The questions behind these errors get a lot of traffic. On Stack Overflow, How can I create a database for a MongoDB container on startup? had 325,066 views that day and How to enable authentication on MongoDB through Docker? had 316,972.…