Check out the solution in the video MongoDB Error: Couldn't Connect To Server [IP]:[Port [path] Exception. As we review in the video, this error is something that we may experience especially on a new setup (very popular in development environments). We solve this error in the video.
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Be careful about using NoSQL solutions in general when they do not apply, or when the data are not best served with them. While NoSQL can be a useful tool, using them with all data sets can lead to significant costs and lower performance. I've seen these solutions over applied, when a SQL database would have been a cheaper alternative. You must understand the data set before using a tool like MongoDB.