Major - P3 Various mongotools (mongodump, mongoexport, mongorestore, mongofiles) disable socket timeouts on their mongodb connections. This allows these tools to work properly on networks with high latencies but it also leaves them vulnerable to blocking forever on "dead" connections. If a connection is dropped uncleanly (without a TCP shutdown) any concurrent read on that socket will continue to block forever. To avoid this, the tools can enable TCP keepalive which sends probes to determine if idles connections are still alive.
It happens that mgo will enable TCP keepalive when a custom dialer is not present (https://github.com/10gen/mgo/blob/1826d82/server.go#L166). Since the mongotools use a custom SSL dialer that does not set keepalive, tools connecting over SSL may block forever if the underlying connection is dropped without a clean TCP shutdown.
The following shows what happens if I shutoff wifi while running mongodump from a host over SSL. (I cancelled the dump after a few minutes otherwise it would hang forever):
$ mongodump --host host.mongodb.net:27017 --authenticationDatabase admin --username user --password pass --ssl --db test 2017-05-15T13:53:53.577-0400 writing test.mongomirror to 2017-05-15T13:53:56.320-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:53:59.321-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:54:02.321-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:54:05.321-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:54:08.320-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:54:11.318-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:54:14.321-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:54:17.318-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:54:20.320-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:54:23.318-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:54:26.319-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:54:29.317-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:54:32.321-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:54:35.318-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:54:38.322-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:54:41.322-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:54:44.321-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:54:47.321-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:54:50.319-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:54:53.322-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:54:56.322-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:54:59.319-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:55:05.322-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:55:08.320-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:55:11.320-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:55:14.317-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:55:17.322-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:55:20.322-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:55:23.320-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:55:26.317-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:55:29.321-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:55:32.317-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:55:35.320-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:55:38.320-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:55:41.321-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:55:44.317-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:55:47.321-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:55:50.320-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:55:53.317-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:55:56.318-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) ^C2017-05-15T13:55:56.624-0400 signal 'interrupt' received; attempting to shut down 2017-05-15T13:55:59.321-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:56:02.320-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) 2017-05-15T13:56:05.317-0400 [#########...............] test.mongomirror 383925/1000000 (38.4%) ^C2017-05-15T13:56:06.599-0400 signal 'interrupt' received; forcefully terminating