No suitable servers found - socket timeout calling ismaster

Question

Hi  
We have a periodical error:  
unable to query db: No suitable servers found (`serverSelectionTryOnce` set):  socket timeout calling ismaster on 'XXXXXX-1.docdb.amazonaws.com:27017'  
  
 in our PHP app, usually 3-4 times per day.   
  
our conditions:  
- app server is in the same region as documentdb  
  
- security group allows the connection (other query runs)  
  
- we have only one instance in the cluster (so I don't understand how this can be connected with ismaster reply from documentdb in case you have multiple instance setup)  
  
- the cloud watch metrics  do not show anything unusual for the time when errors happen, same for the app server  
  
- usually, only one request fails, all others are ok, and the request itself is different (not the same query)  
  
Thank you in advance.

Anva · Answer

The exception explains  connectivity issue between PHP application and the DocumentDB Cluster.

It could be due transient network error or application is exhausting total number of connections or it could be due to load on DocumentDB.  
To rule out the network issue, you can setup a tcpdump if you see any pattern with timing.

Please also provide your exact connection string  and instance details for DocumentDB cluster , would be  great help to investigate.

PHP driver's default behavior only attempts server selection once. If you want ,you can also change this behavior in driver  so that it  can make additional attempts to connect after a socket failure.

No suitable servers found - socket timeout calling ismaster

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