Failed to execute HttpGet for artifact

Products

• CA Release Automation - Release Operations Center (Nolio)
• CA Release Automation - DataManagement Server (Nolio)

Issue/Introduction

While using the "ROC - Get Artifact" action we're receiving the following error:
Artifact [ArtifactTypeName. <artType> ArtifactDefinitionName. <artDefName> Ver. <artVersion>] download failed, Download failed on artifact retrieval agent: Error while downloading artifact from repository artifact - Failed to execute HttpGet for artifact [/nexus/content/repositories/nolio/<path>/<to>/<artifact>] from default repository [https://<repoServerName>:8443/nexus/content/repositories/nolio].

Cause

The artifact was assigned an artifact retrieval agent group. The artifact retrieval agent being used by the deployment is having SSL Handshake errors while retrieving the artifact from the HTTPS repository. In the nolio_all.log file we can see the error:
Error while downloading artifact from repository artifact - Failed to execute HttpGet for artifact [/nexus/content/repositories/nolio/<path>/<to>/<artifact>] from default repository [https://<repoServerName>:8443/nexus/content/repositories/nolio]. 
java.lang.IllegalStateException: Failed to execute HttpGet for artifact ....
... stack trace ...
Caused by: javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target. 

Environment

Release : 6.6

Component : CA Release Automation Release Operations Center

Resolution

Import the needed certificates into the retrieval agent's truststore. 

Additional Information

If you need the specific steps for how to import the needed certificate into the agent's truststore - one of both of these KB articles will help:
javax.net.ssl.SSLHandshakeException PKIX path building failed
Failed to download artifact to retrieval agent