No suitable servers found: `serverSelectionTimeoutMS` expired: [socket timeout calling hello on '[myserver]:27017']

[Hippolyte-wia]

Bug Report

I am migrating my mongo databases from my local server to a managed MongoDB on DigitalOcean.
Everything worked fine on my server, but since I migrated all my dbs to the managed mongo server, nothing works anymore.
I always have the same error in my PHP script :

Fatal error: Uncaught MongoDB\Driver\Exception\ConnectionTimeoutException: No suitable servers found: `serverSelectionTimeoutMS` expired: [socket timeout calling hello on '[myserver]:27017'] in [myserverpath]/finder2.php:41

Stack trace:
#0 [myserverpath]/finder2.php(41): MongoDB\Driver\Manager->executeCommand('db', Object(MongoDB\Driver\Command))
#1 {main} thrown in [myserverpath]/finder2.php on line 41

The only thing I changed is the connection string.
For information, I can connect to the new server with Mongo shell on the same server as the PHP script.

Environment

PHP Version : 7.4.30

Extension informations :
libbson bundled version => 1.20.0
libmongoc bundled version => 1.20.0
libmongoc SSL => enabled
libmongoc SSL library => OpenSSL
libmongoc crypto => enabled
libmongoc crypto library => libcrypto
libmongoc crypto system profile => disabled
libmongoc SASL => enabled
libmongoc ICU => enabled
libmongoc compression => enabled
libmongoc compression snappy => disabled
libmongoc compression zlib => enabled
libmongoc compression zstd => disabled
libmongocrypt bundled version => 1.3.0
libmongocrypt crypto => enabled
libmongocrypt crypto library => libcrypto
mongodb.debug => no value => no value
mongodb.mock_service_id => Off => Off

MongoDB :
Version : MongoDB 5
I don't really know the configuration since it's DigitalOcean who manage everything.
I have the fully managed version with the first configuration and no other options.
The config : 1 GB RAM / 1vCPU / 15 GB Disk / Primary only / AMS3 - MongoDB 5

Test Script

$client = new MongoDB\Driver\Manager(
	'mongodb+srv://[user]:[password]@[doserver]/admin',
	[
		"serverSelectionTryOnce" => false,
		"serverSelectionTimeoutMS" => 5000,
		"tls" => true,
		"ssl" => true,
		"replicaSet" => "db-mongodb-ams3-19362"
	]
);
$command = new MongoDB\Driver\Command(['ping' => 1]);
$client->executeCommand('db', $command);

var_dump($client->getServers());

I tried multiple value for "serverSelectionTimeoutMS" but nothing changes...

Expected and Actual Behavior

Expected Behavior :
The PHP script connects to the DigitalOcean database.

Actual Behavior :
Every time I try to make a request to the new server, it fails with the same error.

Any help on this would be appreciated !

[jmikola]

I tried multiple value for "serverSelectionTimeoutMS" but nothing changes...

Some feedback on your URI:

• ssl is a deprecated alias of tls, so you need not specify both

• serverSelectionTryOnce=false should not generally be necessary since the extension supports retryable reads and writes by default. Leaving this disabled should allow the driver to fail sooner, which may be preferable in an application where you might want to yield an error to the client ASAP w/o blocking the PHP worker.

  That said, if you do want to disable tryOnce behavior (i.e. rely on a server selection loop) and you're connecting to a replica set, you may want to ensure that serverSelectionTimeoutMS is at least as long as the expected time for a failover election to complete. Replica Set Elections conservatively suggests 12 seconds, but five seconds is likely too short.

  This advice isn't relevant for sharded clusters, since mongos insulates the driver from directly dealing with replica set elections. For a sharded cluster connection, you can get by with a much lower serverSelectionTimeoutMS.

For information, I can connect to the new server with Mongo shell on the same server as the PHP script.

If this is the case, it's likely that your PHP environment (or some related firewall configuration) is not allowing outgoing connections. This is commonly caused by SELinux if you'd like to research that further.

If you'd like to test an outgoing connection without using the PHP driver, you can experiment with a Connection Tester script I developed last year. Two shortcomings with the current version of that tool:

• It does not yet support SRV URIs, so you'll need to get a non-SRV URI for the cluster (assuming DigitalOcean provides that)
• It does not yet detect the tls URI option, so you'll need to ensure ssl is included in the connection string

Assuming you can get a non-SRV URI, the README should be enough to get you started. In summary, the script takes a MongoDB connection string and issues an isMaster command (older equivalent of hello) using raw PHP socket functions instead of the mongodb extension. If that also fails to establish a connection to the server it's very likely that you're dealing with a PHP environment issue and nothing to do with the driver itself.

Even if you can't get a non-SRV URI from DigitalOcean, you may be able to create one using the host in the exception message (e.g. "myserver"), since that's coming from a connection attempt in the driver after SRV records have been resolved for initial DNS seedlist discovery. For example:

mongodb://<user>:<password>@<server>:27017/admin?ssl=true&replicaSet=db-mongodb-ams3-19362

That should be a viable URL to feed into the connect.php script.

[Hippolyte-wia]

Thanks for your fast response !

It does not yet support SRV URIs, so you'll need to get a non-SRV URI for the cluster (assuming DigitalOcean provides that)

Unfortunately DigitalOcean does not provide a non-SRV URI and I tried to connect without it (with Mongo Compass) but it doesn't seem to work.

I used your script with the URI exemple you provided and got this error :

Found 1 host(s) in the URI. Will attempt to connect to each. Could not connect to <server>:27017: php_network_getaddresses: getaddrinfo failed: Name or service not known

EDIT :
I tried all my scripts on a local server on my computer and everything works fine, so it might come from the server configuration...
I checked and the port 27017 is open (inbound & outbound) for the TCP protocol on the server.

Is there any default configuration I could try ?

[Hippolyte-wia]

I found out that the port wasn't open on our host's firewall. Everything works fine now!

Thank you for your help!