MID Server communications

MID Server communications happen through an External Communications Channel (ECC) queue. One way to think about the ECC queue is like an airline check-in kiosk. MID Servers check each of these kiosks on a regular basis to see if there are any activities that need to be performed. If there is any activity then MID Server does the job and sends the information back to the ECC queue, which is utilized by the ServiceNow instance to use. ECC queue is an integration point between other systems and the ServiceNow instance. ECC queue is a table in the ServiceNow database that stores messages that are entered through other systems. Messages are classified as output and input messages:

• Output messages: Messages from the ServiceNow instance to some other system
• Input messages: Messages from other systems to the ServiceNow instance

The MID Server subscribes to messages published by the Asynchronous Message Bus (AMB), which notifies the MID Server that it has pending tasks in the ECC queue.

The MID Server opens a persistent connection to the instance through the AMB and listens on the /mid/server/<mid_sys_id | AMB channel. When an output record is inserted into the queue [ecc_queue] table, an AMB message is sent to the MID Server's channel. The MID Server receives this message and immediately polls the ecc_queue table for work.

The MID Server polls the ECC queue on the regular intervals defined in the mid.poll.time configuration parameter, regardless of AMB message activity. The default polling interval is set to 40 seconds, but it can be reconfigured. This polling of the ECC queue at a regular interval is done in case the AMB connection is dropped.

Source: wiki.servicenow.com