Thank you for the replies, Clinton, Kimchy.
Here are answers to your questions:
How many documents (and of what size) are you bulk indexing in a single request?
I limit up to 100 indexings or deletions in a bulk.
70 indices running on how many nodes?
I have 13 nodes.
Also, it seems like the timeout is not coming from elasticsearch itself, but from the client library you are using? If its the Java client, do you execute the bulk with a timeout?
The exception is caught by my code. It is thrown by the following code:
BulkRequestBuilder req = client.prepareBulk();
req.add(...); // up to 100 times