How ESP and its agents retry connections after the address changes?

Products

• ESP Workload Automation

Issue/Introduction

For DR tests, we will not change the DNS name used by the ESP and agents, but the associated IP addresses will be changed.

How ESP and its agents retry connections after the address changes? Will they reach DNS server to resolve to the new IP addresses?

Environment

Release : 12.0

Resolution

When ESP needs to send a request to an agent, it will check the agent address in AGENTDEF table (the loaded copy by LOADAGDF command). If it's a DNS name, then it will enquiry DNS server to resolve it to an IP address and send to the proper address. In other words, by default, every time (including retries for failed connections) ESP will use the DNS name if it's used as the agent address. 

For better performance, you can set INET with HOST_CACHE TTL, so that ESP will use the resolved IP address in the time frame of the TTL. You can change the TTL to 0 when the DNS address will be resolved to a different IP address.

The agent behaves similarly, it will ask the DNS server to resolve it to proper IP address when building a connection to ESP every time including retries. 

However each time DNS call is made, the DNS sends back TTL (time to live), which can 2 mins to 2 weeks.. if the TTL expires, then OS will make DNS call again. Agent itself has absolutely no control over it.  Agent simply tries to connect to ESP.

In order to use the new/current IP address, MGRADDR command can be issued from ESP to redirect agents, so that they will use the new address on their next retries.

Additional Information

See more about ESP INET command on the doc link below:
https://techdocs.broadcom.com/us/en/ca-mainframe-software/automation/ca-workload-automation-esp-edition/12-0/reference/commands/inet-command-manipulate-tcp-ip-attributes.html