How to configure API Gateway

[landorg]

Hi.
I am struggling to configure our kong api gateway to work with the graphdb cluster setup.
AFAICS it should forward things like that:
(if graphdb.workbench.subpath is /graphdb)

example.com/graphdb(.*)  ->  <internal-ip:port><\1 (capture group one)>
example.com/graphdb/index.html  ->  <internal-ip:port>/index.html

am I getting this right?
I disabled the default ingress and created one manually to be able to set the proper kong regex prefix:

{
          path: "/~/graphdb(.*)"
...
}

and then replace it with:

{
    uri: "$(uri_captures[1])"
...
}

imo this should be working but I get a 500 and:

[ERROR] 2023-02-07 18:12:03,714 [http-nio-7200-exec-1 \| c.o.g.p.ClusterProxyServlet] Request to http://index.html failed.
--
Tue, Feb 7 2023 7:12:03 pm | java.net.UnknownHostException: index.html: Name does not resolve
Tue, Feb 7 2023 7:12:03 pm | at java.base/java.net.Inet4AddressImpl.lookupAllHostAddr(Native Method)
Tue, Feb 7 2023 7:12:03 pm | at java.base/java.net.InetAddress$PlatformNameService.lookupAllHostAddr(InetAddress.java:929)
Tue, Feb 7 2023 7:12:03 pm | at java.base/java.net.InetAddress.getAddressesFromNameService(InetAddress.java:1529)
Tue, Feb 7 2023 7:12:03 pm | at java.base/java.net.InetAddress$NameServiceAddresses.get(InetAddress.java:848)
Tue, Feb 7 2023 7:12:03 pm | at java.base/java.net.InetAddress.getAllByName0(InetAddress.java:1519)
Tue, Feb 7 2023 7:12:03 pm | at java.base/java.net.InetAddress.getAllByName(InetAddress.java:1378)
Tue, Feb 7 2023 7:12:03 pm | at java.base/java.net.InetAddress.getAllByName(InetAddress.java:1306)
Tue, Feb 7 2023 7:12:03 pm | at org.apache.http.impl.conn.SystemDefaultDnsResolver.resolve(SystemDefaultDnsResolver.java:45)
Tue, Feb 7 2023 7:12:03 pm | at org.apache.http.impl.conn.DefaultHttpClientConnectionOperator.connect(DefaultHttpClientConnectionOperator.java:112)
Tue, Feb 7 2023 7:12:03 pm | at org.apache.http.impl.conn.PoolingHttpClientConnectionManager.connect(PoolingHttpClientConnectionManager.java:376)
Tue, Feb 7 2023 7:12:03 pm | at org.apache.http.impl.execchain.MainClientExec.establishRoute(MainClientExec.java:393)
Tue, Feb 7 2023 7:12:03 pm | at org.apache.http.impl.execchain.MainClientExec.execute(MainClientExec.java:236)
Tue, Feb 7 2023 7:12:03 pm | at org.apache.http.impl.execchain.ProtocolExec.execute(ProtocolExec.java:186)
Tue, Feb 7 2023 7:12:03 pm | at org.apache.http.impl.execchain.RetryExec.execute(RetryExec.java:89)
Tue, Feb 7 2023 7:12:03 pm | at org.apache.http.impl.execchain.RedirectExec.execute(RedirectExec.java:110)
Tue, Feb 7 2023 7:12:03 pm | at org.apache.http.impl.client.InternalHttpClient.doExecute(InternalHttpClient.java:185)
Tue, Feb 7 2023 7:12:03 pm | at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:83)
Tue, Feb 7 2023 7:12:03 pm | at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:108)
Tue, Feb 7 2023 7:12:03 pm | at com.ontotext.graphdb.http.ServletProxy.proxyRequestWithAuthentication(ServletProxy.java:132)
Tue, Feb 7 2023 7:12:03 pm | at com.ontotext.graphdb.proxy.ClusterProxyBean.handleRequest(ClusterProxyBean.java:99)
Tue, Feb 7 2023 7:12:03 pm | at com.ontotext.graphdb.proxy.ClusterProxyServlet.handleRequest(ClusterProxyServlet.java:47)
Tue, Feb 7 2023 7:12:03 pm | at com.ontotext.graphdb.proxy.ClusterProxyServlet.service(ClusterProxyServlet.java:43)
Tue, Feb 7 2023 7:12:03 pm | at javax.servlet.http.HttpServlet.service(HttpServlet.java:779)
Tue, Feb 7 2023 7:12:03 pm | at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:227)
Tue, Feb 7 2023 7:12:03 pm | at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
Tue, Feb 7 2023 7:12:03 pm | at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:177)
Tue, Feb 7 2023 7:12:03 pm | at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97)
Tue, Feb 7 2023 7:12:03 pm | at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541)
Tue, Feb 7 2023 7:12:03 pm | at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:135)
Tue, Feb 7 2023 7:12:03 pm | at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
Tue, Feb 7 2023 7:12:03 pm | at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78)
Tue, Feb 7 2023 7:12:03 pm | at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:360)
Tue, Feb 7 2023 7:12:03 pm | at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:399)
Tue, Feb 7 2023 7:12:03 pm | at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
Tue, Feb 7 2023 7:12:03 pm | at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:891)
Tue, Feb 7 2023 7:12:03 pm | at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1784)
Tue, Feb 7 2023 7:12:03 pm | at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
Tue, Feb 7 2023 7:12:03 pm | at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191)
Tue, Feb 7 2023 7:12:03 pm | at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659)
Tue, Feb 7 2023 7:12:03 pm | at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
Tue, Feb 7 2023 7:12:03 pm | at java.base/java.lang.Thread.run(Thread.java:829)

Am I getting this wrong?
Any idea what could be causing this?
Thanks

EDIT
x-forwarded-* headers should in theory be set by kong: https://docs.konghq.com/gateway/latest/how-kong-works/routing-traffic/#proxying-and-upstream-timeouts
I'll confirm this. Which of these are required by your proxy?