Mark,
What are your thoughts on changing the Tomcat codebase to return a 503
instead of a 404 if a context is marked as distributable or if
clustering is enabled and deployed but stopped? When I did searches
years ago on this issue, most people at the time would recommend
adding 404 to the fail_on_status, which is what we did...until I
realized that we were causing our own internal DOS attack when we had
a 404 mistakenly left in our apps; that got me thinking how easy it
would be to make mod_jk thrash by just requesting pages that didn't
exist. It's not a huge issue for us since most of our apps are
authenticated using SAML, so all requests are intercepted before the
request is ever sent to Tomcat, but for our apps that don't require
authentication, it would be easy to exploit any app that had 404 in
the fail_on_status.
--
Thanks,
Dan
On Tue, Jun 20, 2023 at 10:41 AM Dan McLaughlin <d...@djabenterprises.com>
wrote:
>
> 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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