SCM checkout timeout when using HTTP Proxy

Issue

Build hang/timeout during SCM checkout from Jenkins. Checkout works fine from command line.
Slow requests during checkout, for example with Git:

"Handling GET /job/myFolder/job/myJob/descriptorByName/hudson.plugins.git.UserRemoteConfig/checkUrl from 127.0.0.1 : RequestHandlerThread[#123]" Id=12345 RUNNABLE (in native)
    at java.lang.ProcessImpl.waitForInterruptibly(Native Method)
    at java.lang.ProcessImpl.waitFor(ProcessImpl.java:449)
    at hudson.Proc$LocalProc.join(Proc.java:320)
    at hudson.Proc.joinWithTimeout(Proc.java:166)
    at org.jenkinsci.plugins.gitclient.CliGitAPIImpl.launchCommandIn(CliGitAPIImpl.java:1789)
    at org.jenkinsci.plugins.gitclient.CliGitAPIImpl.launchCommandWithCredentials(CliGitAPIImpl.java:1519)
    at org.jenkinsci.plugins.gitclient.CliGitAPIImpl.launchCommandWithCredentials(CliGitAPIImpl.java:1437)
    at org.jenkinsci.plugins.gitclient.CliGitAPIImpl.launchCommandWithCredentials(CliGitAPIImpl.java:1428)
    ...

Environment

Jenkins
Jenkins LTS
CloudBees Jenkins Enterprise
Git Plugin
Team Foundation Server Plugin

Resolution

This could be due to the proxy configuration in Jenkins. Some SCM plugins provide support for the HTTP proxy server configured in Jenkins. You can check on the list in the article Jenkins Behind Proxy.

To solve/troubleshoot this, you can add wildcards to the No Proxy Host under Manage Jenkins Manage Plugins Advanced HTTP Proxy Configuration to exclude repository URLs from the proxy.

For example, I do not want to use the HTTP proxy to checkout GitHub repositories, I can add the wildcard *github.com to the No Proxy Host section: