So I tried to create a Valve to check to see if the application is stopped
and convert the 404 response to a 503, but I haven't had any luck getting
it to work. Is there another internal API that I should be using?
context.getState().isAvailable
ways seems to report the app is available even though it's stopped.
import org.apache.catalina.*;
import org.apache.catalina.connector.Request;
import org.apache.catalina.connector.Response;
import org.apache.catalina.valves.ValveBase;
import jakarta.servlet.ServletException;
import java.io.IOException;
import java.util.logging.Logger;
import java.util.logging.Level;
public class DownForMaintenanceValve extends ValveBase {
// Create a Logger
private static final Logger log = Logger.getLogger(DownForMaintenanceValve.
class.getName());
public DownForMaintenanceValve() {
log.info("DownForMaintenanceValve started");
}
@Override
public void invoke(Request request, Response response) throws
IOException, ServletException
{
Context context = request.getContext();
if (!context.getState().isAvailable()) {
log.info("Application is not available, sending 503");
response.sendError(503);
} else {
log.fine("Application is available, passing to next valve");
getNext().invoke(request, response);
}
}
}
--
Thanks,
Dan
On Wed, Jun 14, 2023 at 2:32 PM Mark Thomas <ma...@apache.org> wrote:
> On 14/06/2023 19:49, Dan McLaughlin wrote:
> > Hello,
> >
> > This is probably a question that would be better suited for the dev list,
> > but I thought I'd start here first.
>
> That depends. It is generally better to start on the users list.
>
> > Does anyone understand the reasoning behind why Tomcat, when clustered,
> > throws an HTTP status 404 and not a 503 when you have an application
> > deployed but stopped or paused?
>
> The issue you describe only affects stopped applications. If an
> application is paused then any requests to that application should be
> held until the application is unpaused (or the client timeouts out).
>
> The current Tomcat Mapper dates back to at least Tomcat 4. It might be
> earlier but I don't know the Tomcat 3 code well enough to find the
> Tomcat 3 mapping code in the web interface and I'm not curious enough to
> check the code out so I can use grep.
>
> The clustering implementation dates back to Tomcat 5.
>
> You'll need to dig through the archives to see if this topic was ever
> raised and, if it was, the result of that discussion. Probably around
> the time clustering was added.
>
> > I think I understand that my only option is to
> > failover for 404s considering the current implementation.
>
> That might cause problems. If the node returning 404 is marked as down
> you'll have a DoS vulnerability that is trivial to exploit.
>
> > I've looked to
> > see if there was a configuration setting related to clustering that would
> > allow me to change the behavior, and I couldn't find one; the only
> solution
> > seems to be to write a custom listener that detects that an application
> is
> > deployed but stopped or paused, and then throw a 503 instead.
>
> That would be a better short-term solution and fairly simple to write.
> I'd probably do it as a Valve as you'll get access to Tomcat's internals
> that way.
>
> The clustering implementation generally assumes that all applications
> are available on all nodes. If that isn't the case I wouldn't be
> surprised to see log messages indicating issues with replication.
>
> What is the use case for stopping one (or more) web applications on a node?
>
> Mark
>
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