Monitoring
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The driver allows the application to be notified when certain events happen. These events are organized into the following categories:
Command monitoring
Topology lifecycle
Server lifecycle
Server heartbeats
Connection pools and connections
Topology and server events are part of Server Discovery and Monitoring (SDAM).
Command Monitoring
All user-initiated commands that are sent to the server publish events that
can be subscribed to for fine grained information. The monitoring API
publishes a guaranteed start event for each command, then either a succeeded
or a failed event. A subscriber must implement 3 methods: started
,
succeeded
, and failed
, each which takes a single parameter for
the event. The following is an example logging subscriber based on a
logging subscriber used internally by the driver:
class CommandLogSubscriber include Mongo::Loggable def started(event) # The default inspection of a command which is a BSON document gets # truncated in the middle. To get the full rendering of the command, the # ``to_json`` method can be called on the document. log_debug("#{prefix(event)} | STARTED | #{format_command(event.command.to_json)}") end def succeeded(event) log_debug("#{prefix(event)} | SUCCEEDED | #{event.duration}s") end def failed(event) log_debug("#{prefix(event)} | FAILED | #{event.message} | #{event.duration}s") end private def logger Mongo::Logger.logger end def format_command(args) begin args.inspect rescue Exception '<Unable to inspect arguments>' end end def format_message(message) format("COMMAND | %s".freeze, message) end def prefix(event) "#{event.address.to_s} | #{event.database_name}.#{event.command_name}" end end
To register a custom subscriber, you can do so globally for all clients or on a per-client basis:
subscriber = CommandLogSubscriber.new Mongo::Monitoring::Global.subscribe(Mongo::Monitoring::COMMAND, subscriber) client = Mongo::Client.new([ '127.0.0.1:27017' ], :database => 'test' ) client.subscribe( Mongo::Monitoring::COMMAND, subscriber )
Sample output:
D, [2018-09-23T13:47:31.258020 #4692] DEBUG -- : COMMAND | 127.0.0.1:27027 | test.hello | STARTED | {"hello"=>1, "$readPreference"=>{"mode"=>"primary"}, "lsid"=>{"id"=><BSON::Binary:0x47111693353080 type=uuid data=0x730341e880dc40a2...>}} D, [2018-09-23T13:47:31.259145 #4692] DEBUG -- : COMMAND | 127.0.0.1:27027 | test.hello | SUCCEEDED | 0.000791175s
Server Discovery And Monitoring
The Ruby driver implements Server Discovery And Monitoring (SDAM) specification. and makes the following events available to the application:
Topology opening
Server opening
Server description changed
Topology changed
Server closed
Topology closed
Heartbeat events (covered below in a separate section)
For all events other than the heartbeat events, the succeeded
method
will be called on each event subscriber with the event as the sole argument.
Available data for events varies, therefore to log the events a separate
class is needed for each event type. A simple SDAM logging subscriber
can look like the following:
class SDAMLogSubscriber include Mongo::Loggable def succeeded(event) log_debug(format_event(event)) end private def logger Mongo::Logger.logger end def format_message(message) format("SDAM | %s".freeze, message) end end class TopologyOpeningLogSubscriber < SDAMLogSubscriber private def format_event(event) "Topology type '#{event.topology.display_name}' initializing." end end class ServerOpeningLogSubscriber < SDAMLogSubscriber private def format_event(event) "Server #{event.address} initializing." end end class ServerDescriptionChangedLogSubscriber < SDAMLogSubscriber private def format_event(event) "Server description for #{event.address} changed from " + "'#{event.previous_description.server_type}' to '#{event.new_description.server_type}'." end end class TopologyChangedLogSubscriber < SDAMLogSubscriber private def format_event(event) if event.previous_topology != event.new_topology "Topology type '#{event.previous_topology.display_name}' changed to " + "type '#{event.new_topology.display_name}'." else "There was a change in the members of the '#{event.new_topology.display_name}' " + "topology." end end end class ServerClosedLogSubscriber < SDAMLogSubscriber private def format_event(event) "Server #{event.address} connection closed." end end class TopologyClosedLogSubscriber < SDAMLogSubscriber private def format_event(event) "Topology type '#{event.topology.display_name}' closed." end end
To subscribe to SDAM events globally:
topology_opening_subscriber = TopologyOpeningLogSubscriber.new server_opening_subscriber = ServerOpeningLogSubscriber.new server_description_changed_subscriber = ServerDescriptionChangedLogSubscriber.new topology_changed_subscriber = TopologyChangedLogSubscriber.new server_closed_subscriber = ServerClosedLogSubscriber.new topology_closed_subscriber = TopologyClosedLogSubscriber.new Mongo::Monitoring::Global.subscribe(Mongo::Monitoring::TOPOLOGY_OPENING, topology_opening_subscriber) Mongo::Monitoring::Global.subscribe(Mongo::Monitoring::SERVER_OPENING, server_opening_subscriber) Mongo::Monitoring::Global.subscribe(Mongo::Monitoring::SERVER_DESCRIPTION_CHANGED, server_description_changed_subscriber) Mongo::Monitoring::Global.subscribe(Mongo::Monitoring::TOPOLOGY_CHANGED, topology_changed_subscriber) Mongo::Monitoring::Global.subscribe(Mongo::Monitoring::SERVER_CLOSED, server_closed_subscriber) Mongo::Monitoring::Global.subscribe(Mongo::Monitoring::TOPOLOGY_CLOSED, topology_closed_subscriber)
Subscribing to SDAM events for a single client is a little more involved since the events may be published during the client's construction:
topology_opening_subscriber = TopologyOpeningLogSubscriber.new server_opening_subscriber = ServerOpeningLogSubscriber.new server_description_changed_subscriber = ServerDescriptionChangedLogSubscriber.new topology_changed_subscriber = TopologyChangedLogSubscriber.new server_closed_subscriber = ServerClosedLogSubscriber.new topology_closed_subscriber = TopologyClosedLogSubscriber.new sdam_proc = Proc.new do |client| client.subscribe(Mongo::Monitoring::TOPOLOGY_OPENING, topology_opening_subscriber) client.subscribe(Mongo::Monitoring::SERVER_OPENING, server_opening_subscriber) client.subscribe(Mongo::Monitoring::SERVER_DESCRIPTION_CHANGED, server_description_changed_subscriber) client.subscribe(Mongo::Monitoring::TOPOLOGY_CHANGED, topology_changed_subscriber) client.subscribe(Mongo::Monitoring::SERVER_CLOSED, server_closed_subscriber) client.subscribe(Mongo::Monitoring::TOPOLOGY_CLOSED, topology_closed_subscriber) end client = Mongo::Client.new(['127.0.0.1:27017'], database: 'test', sdam_proc: sdam_proc)
Sample output:
D, [2018-10-09T13:58:03.489461 #22079] DEBUG -- : SDAM | Topology type 'Unknown' initializing. D, [2018-10-09T13:58:03.489699 #22079] DEBUG -- : SDAM | Server 127.0.0.1:27100 initializing. D, [2018-10-09T13:58:03.491384 #22079] DEBUG -- : SDAM | Server description for 127.0.0.1:27100 changed from 'unknown' to 'unknown'. D, [2018-10-09T13:58:03.491642 #22079] DEBUG -- : SDAM | Server localhost:27100 initializing. D, [2018-10-09T13:58:03.493199 #22079] DEBUG -- : SDAM | Server description for localhost:27100 changed from 'unknown' to 'primary'. D, [2018-10-09T13:58:03.493473 #22079] DEBUG -- : SDAM | Server localhost:27101 initializing. D, [2018-10-09T13:58:03.494874 #22079] DEBUG -- : SDAM | Server description for localhost:27101 changed from 'unknown' to 'secondary'. D, [2018-10-09T13:58:03.495139 #22079] DEBUG -- : SDAM | Server localhost:27102 initializing. D, [2018-10-09T13:58:03.496504 #22079] DEBUG -- : SDAM | Server description for localhost:27102 changed from 'unknown' to 'secondary'. D, [2018-10-09T13:58:03.496777 #22079] DEBUG -- : SDAM | Topology type 'Unknown' changed to type 'ReplicaSetNoPrimary'. D, [2018-10-09T13:58:03.497306 #22079] DEBUG -- : SDAM | Server 127.0.0.1:27100 connection closed. D, [2018-10-09T13:58:03.497606 #22079] DEBUG -- : SDAM | Topology type 'ReplicaSetNoPrimary' changed to type 'ReplicaSetWithPrimary'. # client.close D, [2018-10-09T13:58:05.342057 #22079] DEBUG -- : SDAM | Server localhost:27100 connection closed. D, [2018-10-09T13:58:05.342299 #22079] DEBUG -- : SDAM | Server localhost:27101 connection closed. D, [2018-10-09T13:58:05.342565 #22079] DEBUG -- : SDAM | Server localhost:27102 connection closed. D, [2018-10-09T13:58:05.342693 #22079] DEBUG -- : SDAM | Topology type 'ReplicaSetWithPrimary' closed.
Note
:sdam_proc
client option applies only to the client during whose
construction it is given. When certain client options are changed via the
Client#with
call, a new cluster may be created by the driver with
a default set of event subscribers. If this happens, the provided
:sdam_proc
is not called and the application may miss events.
Server Heartbeats
The application can be notified of each server heartbeat by subscribing
to SERVER_HEARTBEAT topic. A server heartbeat listener must implement
three methods: started
, succeeded
and failed
. Each heartbeat
invokes the started
method on the listener, and then either succeeded
or failed
method depending on the outcome of the heartbeat.
All heartbeat events contain the address of the server that the heartbeat was sent to. Succeeded and failed events contain the round trip time for the hello or legacy hello command. Failed event also contains the exception instance that was raised during hello or legacy hello command execution. Please review the API documentation for ServerHeartbeatStarted, ServerHeartbeatSucceeded and ServerHeartbeatFailed for event attribute details.
The following is an example logging heartbeat event subscriber:
class HeartbeatLogSubscriber include Mongo::Loggable def started(event) log_debug("#{event.address} | STARTED") end def succeeded(event) log_debug("#{event.address} | SUCCEEDED | #{event.duration}s") end def failed(event) log_debug("#{event.address} | FAILED | #{event.error.class}: #{event.error.message} | #{event.duration}s") end private def logger Mongo::Logger.logger end def format_message(message) format("HEARTBEAT | %s".freeze, message) end end
Similarly to command events, the application can subscribe to heartbeat events globally or for a specific client:
subscriber = HeartbeatLogSubscriber.new Mongo::Monitoring::Global.subscribe(Mongo::Monitoring::SERVER_HEARTBEAT, subscriber) client = Mongo::Client.new([ '127.0.0.1:27017' ], :database => 'test' ) client.subscribe( Mongo::Monitoring::SERVER_HEARTBEAT, subscriber )
Sample output:
D, [2018-09-23T13:44:10.707018 #1739] DEBUG -- : HEARTBEAT | 127.0.0.1:27027 | STARTED D, [2018-09-23T13:44:10.707778 #1739] DEBUG -- : HEARTBEAT | 127.0.0.1:27027 | SUCCEEDED | 0.000772381s
Heartbeat Event Intervals
When connected to MongoDB 4.2 and earlier servers, Ruby driver by default
issues heartbeats every :heartbeat_frequency
(Ruby client option) seconds,
and heartbeats are non-overlapping (the succeeded event for a heartbeat is
guaranteed to be published before the started event for the next heartbeat is
published). When connected to MongoDB 4.4 and later servers, the driver uses
multiple monitoring threads and a more complex heartbeat protocol designed
to detect changes in server state quicker; as a result, heartbeat event
intervals can be more irregular and heartbeat events can overlap. Specifically,
an awaited heartbeat can start or finish while a non-awaited heartbeat
is in progress, and vice versa. Use the ServerHeartbeatStarted#awaited?
,
ServerHeartbeatSucceeded#awaited?
and ServerHeartbeatFailed#awaited?
methods to distinguish between non-awaited and awaited heartbeats.
When a client is attempting to perform an operation and it does not have a suitable server, the deployment is scanned more frequently - each server can be polled up to every 500 milliseconds. It is also possible for the application to request a manual scan of a particular server; the driver enforces the 500 millisecond minimum interval between scans.
Connection Pool And Connection Monitoring
Each client maintains a connection pool for each server in the deployment that
it is aware of, and publishes events for both connection pools and individual
connections. To subscribe to these events, define a subscriber class implementing
the method pubished
which takes a single parameter for the event that
is being published. Note that future versions of the driver may introduce
additional events published through this mechanism.
The following events are currently implemented by the driver, following the CMAP specification:
PoolCreated
PoolCleared
PoolClosed
ConnectionCreated
ConnectionReady
ConnectionClosed
ConnectionCheckOutStarted
ConnectionCheckOutFailed
ConnectionCheckOutSucceeded
ConnectionCheckedIn
The driver provides a logging subscriber which may be used to log all connection pool and connection-related events. This subscriber is not enabled by default because it will create log entries for each operation performed by the application. To enable this subscriber globally or per client:
Mongo::Monitoring::Global.subscribe( Mongo::Monitoring::CONNECTION_POOL, Mongo::Monitoring::CmapLogSubscriber.new) client = Mongo::Client.new([ '127.0.0.1:27017' ], :database => 'test' ) subscriber = Mongo::Monitoring::CmapLogSubscriber.new client.subscribe( Mongo::Monitoring::CONNECTION_POOL, subscriber )
Sample output:
D, [2019-05-06T17:23:21.595412 #8576] DEBUG -- : MONGODB | EVENT: #<PoolCreated address=127.0.0.1:27741 options={...}> D, [2019-05-06T17:23:21.595584 #8576] DEBUG -- : MONGODB | EVENT: #<PoolCleared address=127.0.0.1:27741> D, [2019-05-06T17:23:21.603549 #8576] DEBUG -- : MONGODB | EVENT: #<PoolCreated address=localhost:27741 options={...}> D, [2019-05-06T17:23:21.603616 #8576] DEBUG -- : MONGODB | EVENT: #<ConnectionCheckOutStarted address=localhost:27741> D, [2019-05-06T17:23:21.603684 #8576] DEBUG -- : MONGODB | EVENT: #<ConnectionCreated address=localhost:27741 connection_id=1> D, [2019-05-06T17:23:21.604079 #8576] DEBUG -- : MONGODB | EVENT: #<ConnectionCheckedOut address=localhost:27741 connection_id=1> D, [2019-05-06T17:23:21.605759 #8576] DEBUG -- : MONGODB | EVENT: #<ConnectionReady address=localhost:27741 connection_id=1> D, [2019-05-06T17:23:21.605784 #8576] DEBUG -- : MONGODB | EVENT: #<ConnectionCheckedIn address=localhost:27741 connection_id=1> D, [2019-05-06T17:23:21.605817 #8576] DEBUG -- : MONGODB | EVENT: #<PoolCleared address=localhost:27741> D, [2019-05-06T17:23:21.605852 #8576] DEBUG -- : MONGODB | EVENT: #<ConnectionClosed address=localhost:27741 connection_id=1 reason=stale>
Disabling Monitoring
To turn off monitoring, set the client monitoring option to false
:
client = Mongo::Client.new([ '127.0.0.1:27017' ], :database => 'test', :monitoring => false )
Excluded and Redacted Events
The Ruby driver does not pubish, and occasionaly redacts, some events via the command monitoring mechanism:
If the command belongs to a particular subset of redacted commands, or contains keys that trigger payload redaction, an empty payload will be provided for security reasons. The full payload can be accessed by setting the
MONGO_RUBY_DRIVER_UNREDACT_EVENTS
environment variable to1
,true
oryes
. The following commands are redacted:authenticate
saslStart
saslContinue
getnonce
createUser
updateUser
copydbgetnonce
copydbsaslstart
copydb
If the command is a handshake command, either
ismaster
orhello
, on a non-monitoring connection, no event is published at all.Commands sent over monitoring connections (such as ismaster and hello) do not publish command monitoring events. Instead, every time a server is checked a server heartbeat event is published. The server heartbeat events do not include command or reply payloads.
If the command is a handshake command, and the
speculativeAuthenticate
options istrue
, the command will be redacted, and an empty payload will be provided.