APM - DotNET Agent will not connect to the Introscope Enterprise Manager

Products

• CA Application Performance Management (APM / Wily / Introscope)

Issue/Introduction

New .Net agents are not connecting to the Cluster and are reporting the following exceptions in the .net agent log:

[INFO] [IntroscopeAgent.IsengardServerConnectionManager] Connected controllable Agent to the Introscope Enterprise Manager at 10.xx.xxx.xx:5001,com.wily.isengard.postofficehub.link.net.DefaultSocketFactory. Host = "<host>", Process = ".NET Process", Agent Name = "CreditAgent", Active = "False". 
[INFO] [IntroscopeAgent.ConnectionThread] New list {Collector1Host.fqdn.1@5001, Collector1Host@5001, Collector2Host@5001, Collector3Host.fqdn.1@5001, Collector3Host@5001, Collector2Host@5001, }@1619343532022 downloaded from 10.xx.xxx.xx:5001,com.wily.isengard.postofficehub.link.net.DefaultSocketFactory
[INFO] [IntroscopeAgent.Agent] New list accepted
[WARN] [IntroscopeAgent.IsengardServerConnectionManager] Lost contact with the Introscope Enterprise Manager at 10.xx.xxx.xx:5001.
[WARN] [IntroscopeAgent.ConnectionThread] Failed to connect to the Introscope Enterprise Manager at Collector1Host.fqdn.1:5001,com.wily.isengard.postofficehub.link.net.DefaultSocketFactory (1).
[WARN] [IntroscopeAgent.ConnectionThread] System.Net.Sockets.SocketException (0x80004005): This is usually a temporary error during hostname resolution and means that the local server did not receive a response from an authoritative server
[WARN] [IntroscopeAgent.ConnectionThread] Failed to connect to the Introscope Enterprise Manager at Collector1Host:5001,com.wily.isengard.postofficehub.link.net.DefaultSocketFactory (1).
[WARN] [IntroscopeAgent.ConnectionThread] System.Net.Sockets.SocketException (0x80004005): No such host is known
[WARN] [IntroscopeAgent.ConnectionThread] Failed to connect to the Introscope Enterprise Manager at Collector2Host:5001,com.wily.isengard.postofficehub.link.net.DefaultSocketFactory (1).
[WARN] [IntroscopeAgent.ConnectionThread] System.Net.Sockets.SocketException (0x80004005): No such host is known
[WARN] [IntroscopeAgent.ConnectionThread] Failed to connect to the Introscope Enterprise Manager at Collector3Host.fqdn.1:5001,com.wily.isengard.postofficehub.link.net.DefaultSocketFactory (1).
[WARN] [IntroscopeAgent.ConnectionThread] System.Net.Sockets.SocketException (0x80004005): No such host is known
[WARN] [IntroscopeAgent.ConnectionThread] Failed to connect to the Introscope Enterprise Manager at Collector3Host:5001,com.wily.isengard.postofficehub.link.net.DefaultSocketFactory (1).
[WARN] [IntroscopeAgent.ConnectionThread] System.Net.Sockets.SocketException (0x80004005): This is usually a temporary error during hostname resolution and means that the local server did not receive a response from an authoritative server

Environment

APM 10.7.x

Cause

The MOM passes the list of collectors to the agent with hostnames or fqdn, however the agent is not able to resolve the collectors DNS and therefore it fails to connect. This is a DNS resolution issue.

Resolution

This is due to a DNS resolution issue. 
This particular case was addressed by setting IP address for the collectors (rather than using hostnames).

1.- Open IntroscopeEnterpriseManager.properties file (MOM) and replace:
introscope.enterprisemanager.clustering.login.em1.host=Collector1_Hostname
introscope.enterprisemanager.clustering.login.em2.host=Collector2_Hostname

to:
introscope.enterprisemanager.clustering.login.em1.host=IP_address_Collector1
introscope.enterprisemanager.clustering.login.em2.host=IP_address-Collector2

2.- Restart the MOM for the changes to take effect