White page if ElasticSearch cannot be reached

[matthias-ronge]

If ElasticSearch is not available, after a correct login only an empty page appears, no desktop (also no empty desktop).

An error message appears in the log when the page with the login form is loaded. However, there is no indication that an error has occurred.

[ERROR] 2020-04-22 09:18:47.821 [http-nio-8080-exec-6] IndexingForm - elasticSearchNotRunning
java.net.ConnectException: null
	at org.apache.http.nio.pool.RouteSpecificPool.timeout(RouteSpecificPool.java:168) ~[httpcore-nio-4.4.5.jar:4.4.5]
	at org.apache.http.nio.pool.AbstractNIOConnPool.requestTimeout(AbstractNIOConnPool.java:561) ~[httpcore-nio-4.4.5.jar:4.4.5]
	at org.apache.http.nio.pool.AbstractNIOConnPool$InternalSessionRequestCallback.timeout(AbstractNIOConnPool.java:822) ~[httpcore-nio-4.4.5.jar:4.4.5]
	at org.apache.http.impl.nio.reactor.SessionRequestImpl.timeout(SessionRequestImpl.java:183) ~[httpcore-nio-4.4.5.jar:4.4.5]
	at org.apache.http.impl.nio.reactor.DefaultConnectingIOReactor.processTimeouts(DefaultConnectingIOReactor.java:210) ~[httpcore-nio-4.4.5.jar:4.4.5]
	at org.apache.http.impl.nio.reactor.DefaultConnectingIOReactor.processEvents(DefaultConnectingIOReactor.java:155) ~[httpcore-nio-4.4.5.jar:4.4.5]
	at org.apache.http.impl.nio.reactor.AbstractMultiworkerIOReactor.execute(AbstractMultiworkerIOReactor.java:348) ~[httpcore-nio-4.4.5.jar:4.4.5]
	at org.apache.http.impl.nio.conn.PoolingNHttpClientConnectionManager.execute(PoolingNHttpClientConnectionManager.java:192) ~[httpasyncclient-4.1.2.jar:4.1.2]
	at org.apache.http.impl.nio.client.CloseableHttpAsyncClientBase$1.run(CloseableHttpAsyncClientBase.java:64) ~[httpasyncclient-4.1.2.jar:4.1.2]
	at java.lang.Thread.run(Thread.java:748) [?:1.8.0_144]

Error message after login:

Apr 22, 2020 9:18:48 AM org.apache.myfaces.lifecycle.RenderResponseExecutor execute
WARNUNG: There are some unhandled FacesMessages, this means not every FacesMessage had a chance to be rendered.
These unhandled FacesMessages are: 
- 
[ERROR] 2020-04-22 09:24:29.679 [http-nio-8080-exec-7] CustomLoginSuccessHandler - java.net.ConnectException

You have to log in first to realize that you are stuck. Reconnect is not attempted, Tomcat has to be restarted.

Goal: An error message should be displayed on the login form. (The login might be locked.) The next time you try, Production should try to connect again without you having to restart Tomcat.

[Kathrin-Huber]

You doesn't have to restart tomcat. It's sufficient to enter the root url again.
Then you see this:

The redirection to the desktop is somehow missing here

[solth]

Instead of redirecting to a broken desktop with an error message I would suggest to display the same error message popup that is shown when a user without administrative privileges logs into a system with an out-of-date index (see #2928)

[matthias-ronge]

I can confirm that I get the desktop (but empty, and takes a long time − timeouts?) when I manually truncate the URL in the browser window; and after starting ElasticSearch it reconnects! Maybe this was fixed meanwile, I update the issue description. However, the suggestion of @solth is the best fit here.