Mongo Atlas - Low connection limit?

Question

I am currently testing a free tier of mongo atlas, however I am repeatedly running into issues with the connection limit (100 on the free tier).

I am using the database in an Azure Service Fabric application that has many services and will run on multiple nodes (although currently I am mostly just running locally using a single node local cluster).

To me, 100 connections seems extremely low, I understand it is a free tier, but even the lower tier paid clusters have a low limit (https://docs.atlas.mongodb.com/connection-limits/). My production cluster would likely be M20 to start with which has a limit of 700.

I currently have no confidence at all using Mongo Atlas for my production cluster as I am worried I will run out of connections.

I previously had a cluster with mLab (at a previous job) which had a limit of around 16000 connections on all clusters (and ours was usually sat at around ~800).

I am using the C# driver which I have read I do not need to do anything specific to close the connections. However I have found sometimes that I am not running anything locally (not the service or even a GUI) and yet the connections are sat at almost 100, as if open connections are not being closed.

Am I right in thinking these limits are very restrictive? Am I doing something wrong to keep using up my connections?

Update 16/09/2019: I have spoken to Mongo about this and got the following reply: Our connection limits are set conservatively to ensure that memory exhaustion does not lead to stability problems for your MongoDB Atlas cluster. However, we are in fact currently doing some deep testing within our performance team around whether we can safely lift these limits. Please stay tuned for a likely increase of these limits soon.

So it seems this may be changed Soon™

Answer 1

Just to mark this solved: they have twice increased the limits since I posted this.

Now the M20 tier that previously had 700 has 3000 connections, and lower tiers have also been increased. They are now what I would consider "safe" (i.e you would have to be doing something wrong or unusual to hit the limits).