We typically don't deploy a ROOT context in our production
environments--for no other reason than making it more difficult to poke
around. I'll look at that as an option. Thanks for the tips.
--
Thanks,
Dan
On Tue, Jun 20, 2023 at 10:28 AM Mark Thomas <ma...@apache.org> wrote:
> On 20/06/2023 15:41, Dan McLaughlin wrote:
> > 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.
>
> The code is looking at the wrong Context. Since the web application has
> been stopped the request won't be mapped to it. I'm guessing the request
> has been mapped to the root context which is available.
>
> You'll need to do something like:
>
> Container[] containers = request.getHost().findChildren();
> for (Container container : containers) {
> if (container.getState().isAvailable()) {
> continue;
> }
> Context context = (Context) container;
> if (request.getDecodedRequestURI().equals(context.getPath()) ||
> request.getDecodedRequestURI().startsWith(
> context.getPath() + '/')) {
> response.sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE);
> }
> }
>
> I haven't optimised this at all. It isn't particularly efficient. It is
> just to give you an idea.
>
> Actually. I have just had a much better idea. It works by taking
> advantage of the Servlet specification mapping rules which require the
> longest context path match.
>
> Lets assume you have /app1 /app2 and /app3
>
> In your ROOT web application create a maintenance Servlet that just
> returns a 503 and map it to "/app1/*" "/app2/*" and /app3/*".
>
> If app1 is running, the longest context path match rule means it will be
> mapped to /app1 and the application will handle it. If the web
> application is stopped, the request will be mapped to ROOT where it will
> match the maintenance Servlet and return a 503.
>
> The only thing that this won't work for is if you want to take the RROT
> web application out of service.
>
> Mark
>
>
> > 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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> >>
> >>
> >
>
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