mongo-express connection issue with mongo

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I am deploying mongo express on a kubernetes cluster and is not connecting to mongodb container inside the pod. In the mongo-express documentation ithere is a list of variables we need to configure one of which is ME_CONFIG_MONGODB_SERVER to establish the connection. It turns out that when I kubectl exec into the mongo-express container it has an environment variable inside there that is NOT in the documentation and that variable is overriding the connection. The variable is ME_CONFIG_MONGODB_URL=mongodb://mongo:27017. When I set the variable to the same value of the variable ME_CONFIG_MONGODB_SERVER=mongodb-service, it solved the issue.