Why is PyMongo 3 giving ServerSelectionTimeoutError?
I'm using:
- Python 3.4.2
- PyMongo 3.0.2
- mongolab running mongod 2.6.9
- uWSGI 2.0.10
- CherryPy 3.7.0
- nginx 1.6.2
uWSGI start params:
--socket 127.0.0.1:8081 --daemonize --enable-threads --threads 2 --processes 2
I setup my MongoClient ONE time:
self.mongo_client = MongoClient('mongodb://user:[email protected]:port/mydb')
self.db = self.mongo_client['mydb']
I try and save a JSON dict to MongoDB:
result = self.db.jobs.insert_one(job_dict)
It works via a unit test that executes the same code path to mongodb. However when I execute via CherryPy and uWSGI using an HTTP POST, I get this:
pymongo.errors.ServerSelectionTimeoutError: No servers found yet
Why am I seeing this behavior when run via CherryPy and uWSGI? Is this perhaps the new thread model in PyMongo 3?
Update:
If I run without uWSGI and nginx by using the CherryPy built-in server, the insert_one() works.
Update 1/25 4:53pm EST:
After adding some debug in PyMongo, it appears that topology._update_servers() knows that the server_type = 2 for server 'myserver-a.mongolab.com'. However server_description.known_servers() has the server_type = 0 for server 'myserver.mongolab.com'
This leads to the following stack trace:
result = self.db.jobs.insert_one(job_dict)
File "/usr/local/lib/python3.4/site-packages/pymongo/collection.py", line 466, in insert_one
with self._socket_for_writes() as sock_info:
File "/usr/local/lib/python3.4/contextlib.py", line 59, in __enter__
return next(self.gen)
File "/usr/local/lib/python3.4/site-packages/pymongo/mongo_client.py", line 663, in _get_socket
server = self._get_topology().select_server(selector)
File "/usr/local/lib/python3.4/site-packages/pymongo/topology.py", line 121, in select_server
address))
File "/usr/local/lib/python3.4/site-packages/pymongo/topology.py", line 97, in select_servers
self._error_message(selector))
pymongo.errors.ServerSelectionTimeoutError: No servers found yet
We're investigating this problem, tracked in PYTHON-961. You may be able to work around the issue by passing connect=False when creating instances of MongoClient. That defers background connection until the first database operation is attempted, avoiding what I suspect is a race condition between spin up of MongoClient's monitor thread and multiprocess forking.
As mentioned here: https://stackoverflow.com/a/54314615/8953378
I added ?ssl=true&ssl_cert_reqs=CERT_NONE to my connection string, and it fixed the issue.
so instead of:
connection_string = "mongodb+srv://<USER>:<PASSWORD>@<CLUSTER>/<COLLECTION>"
I wrote:
connection_string = "mongodb+srv://<USER>:<PASSWORD>@<CLUSTER>/<COLLECTION>?ssl=true&ssl_cert_reqs=CERT_NONE"
(Note that if you have other parameters in your connection string, you need to change the ? to & )
I fixed it for myself by downgrading from pymongo 3.0 to 2.8. No idea what's going on.
flask/bin/pip uninstall pymongo
flask/bin/pip install pymongo==2.8
I am not sure if you are using the MongoDB paired with AWS Cloud service. But if you are, I found that you have to specify which IP Address you want MongoDB to have access to.
So what you need to do is add the IP Address of your host server to allow entry.
In MongoAtlas, this can be done at this page
I know there was already a solution to the same issue, but I didn't find a solution that helped my situation, so wanted to post this, so others could benefit if they ever face the same problem that I do.