Why do I get an "message len 1347703880 is invalid. Min 16 Max: 48000000" error when trying to connect to an OKD pod running a simple mongo container? - mongodb

Question

I have created a Mongo container using only the base mongo:3.6.4 official docker image and deployed it to my OpenShift OKD cluster, but cannot connect to this MongoDB instance using a Mongo client from outside the cluster.
I can access the pod at http://mongodb.my.domain and successfully get the "It looks like you are trying to access MongoDB over HTTP on the native driver port." message.
When using the terminal on the pod I can successfully log-in using:
mongo "mongodb://mongoadmin:pass#localhost" --authenticationDatabase admin
But when trying to connect from outside OKD the connection fails.
My client needs to pass through a proxy before it can access the OKD pods and I do have a .der certificate file but am unsure if this is related to the issue.
Some commands I have tried:
mongo "mongodb://mongoadmin:pass#mongodb.my.domain:80" --authenticationDatabase admin
mongo --ssl "mongodb://mongoadmin:pass#mongodb.my.domain:80" --authenticationDatabase admin
I expected to be able to connect successfully but instead get this error message:
MongoDB shell version v3.4.20
connecting to: mongodb://mongoadmin:pass#mongodb.my.domain:80
2019-05-15T11:32:25.514+0100 I NETWORK [thread1] recv(): message len 1347703880 is invalid. Min 16 Max: 48000000
2019-05-15T11:32:25.514+0100 E QUERY [thread1] Error: network error while attempting to run command 'isMaster' on host 'mongodb.my.domain:80' :
connect#src/mongo/shell/mongo.js:240:13
#(connect):1:6
exception: connect failed
I am unsure if it an issue with how I am using my MongoDB client or potentially some proxy settings on my OKD cluster. Any help would be appreciated.

Answer 1

The problem here is that external OpenShift routes aren't great at handling database connections. When you attempt to connect to the Mongo pod via the route, the route will accept the connection and transmit your connection to the Mongo service. I believe this transmission wraps the connection in in a HTTP wrapper, which Mongo doesn't like to handle. The OKD documentation highlights that path based route traffic should be HTTP based, which will cause the connection to fail.
You can see evidence of this when trying to connect to a MongoDB database and it returns "It looks like you are trying to access MongoDB over HTTP on the native driver port." to the browser. The user relief.malone explains this and has proposed a couple of solutions / workarounds in their answer to this question.
To add to relief.malone's answer, I would suggest that you port forward from the MongoDB pod to your local machine for development/debugging. In production, you could deploy an application to OKD that references the MongoDB service via it's internal DNS name, which will look something like this: mongodb.project_namespace.svc:27017. This way you will avoid the route interfering with the connection.
The Openshift OKD documentation on port-forwarding isn't that informative, but, since oc runs the kubectl command under the hood, you can read this Kubernetes guide to get some more information