Hi,

I installed CentOS 8 and Docker and Docker compose on top of it. When I Installed Jenkins and tried to login the login works and logs show Jenkins installed successfully. Version is 2.237. 

The next page shows This Jenkins instance appears to be offline. When I checked the logs, get the below exception.

hudson.util.Retrier#start: The attempt #1 to do the action check updates server failed with an allowed exception:
java.net.UnknownHostException: updates.jenkins.io
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:184)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
at java.net.Socket.connect(Socket.java:607)
at sun.security.ssl.SSLSocketImpl.connect(SSLSocketImpl.java:666)
at sun.net.NetworkClient.doConnect(NetworkClient.java:175)
at sun.net.www.http.HttpClient.openServer(HttpClient.java:463)
at sun.net.www.http.HttpClient.openServer(HttpClient.java:558)
at sun.net.www.protocol.https.HttpsClient.<init>(HttpsClient.java:264)
at sun.net.www.protocol.https.HttpsClient.New(HttpsClient.java:367)
at sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.getNewHttpClient(AbstractDelegateHttpsURLConnection.java:191)
at sun.net.www.protocol.http.HttpURLConnection.plainConnect0(HttpURLConnection.java:1162)
at sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:1056)
at sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.connect(AbstractDelegateHttpsURLConnection.java:177)
at sun.net.www.protocol.http.HttpURLConnection.getInputStream0(HttpURLConnection.java:1570)
at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1498)
at sun.net.www.protocol.https.HttpsURLConnectionImpl.getInputStream(HttpsURLConnectionImpl.java:268)
at hudson.model.DownloadService.loadJSON(DownloadService.java:114)
at hudson.model.UpdateSite.updateDirectlyNow(UpdateSite.java:212)
at hudson.model.UpdateSite.updateDirectlyNow(UpdateSite.java:207)
at hudson.PluginManager.checkUpdatesServer(PluginManager.java:1767)
at hudson.util.Retrier.start(Retrier.java:63)
at hudson.PluginManager.doCheckUpdatesServer(PluginManager.java:1738)
at jenkins.DailyCheck.execute(DailyCheck.java:93)
at hudson.model.AsyncPeriodicWork.lambda$doRun$0(AsyncPeriodicWork.java:100)
at java.lang.Thread.run(Thread.java:748)

When I ping updates.jenkins.io get packet loss. When I ping google.com it works. Both from the host and also from the Windows system.

Thanks.