[Bug 63389] Enable Servlet Warmup for Containerization

[bu...@apache.org]

https://bz.apache.org/bugzilla/show_bug.cgi?id=63389

--- Comment #10 from Eugène Adell <eu...@gmail.com> ---
(In reply to Igal Sapir from comment #0)
> Currently, one hack that many use is to launch Tomcat during the container
> build process, wait for an arbitrary length of time, e.g. 10s or 20s, and
> then shut Tomcat down.

From your question and some comments, if the problem is with the "arbitrary
length of time", I suggest to rely on JMX particularly on the Connector
stateName value. It is changing from INITIALIZED to STARTED once Tomcat has
finished deploying. If you can bring ANT within your docker, the effort is not
that huge, you just need 2 targets, one for monitoring the Connector state, and
one for stopping Tomcat.

This is the result that I get with a servlet called at the startup and that
sleeps 60 during its initialization :

catalina.out
09-Jul-2019 22:10:55.804 INFO [localhost-startStop-5]
org.apache.catalina.startup.HostConfig.deployDirectory Deployment of web
application directory
[/home/eadell/tests/apache-tomcat-8.5.15/webapps/host-manager] has finished in
[27] ms
09-Jul-2019 22:10:55.879 FINE [localhost-startStop-4]
org.apache.catalina.authenticator.AuthenticatorBase.startInternal No
SingleSignOn Valve is present
09-Jul-2019 22:10:56.055 INFO [localhost-startStop-4]
org.apache.catalina.startup.HostConfig.deployDirectory Deployment of web
application directory
[/home/eadell/tests/apache-tomcat-8.5.15/webapps/examples] has finished in
[793] ms
09-Jul-2019 22:11:55.779 INFO [localhost-startStop-3]
org.apache.catalina.startup.HostConfig.deployDirectory Deployment of web
application directory
[/home/eadell/tests/apache-tomcat-8.5.15/webapps/slowstart] has finished in
[60,518] ms
09-Jul-2019 22:11:55.790 INFO [main] org.apache.coyote.AbstractProtocol.start
Starting ProtocolHandler ["http-nio-8280"]
09-Jul-2019 22:11:55.811 INFO [main] org.apache.coyote.AbstractProtocol.start
Starting ProtocolHandler ["http-nio-8281"]
09-Jul-2019 22:11:55.815 INFO [main] org.apache.catalina.startup.Catalina.start
Server startup in 60719 ms
09-Jul-2019 22:11:57.411 INFO [main]
org.apache.catalina.core.StandardServer.await A valid shutdown command was
received via the shutdown port. Stopping the Server instance.
09-Jul-2019 22:11:57.412 INFO [main] org.apache.coyote.AbstractProtocol.pause
Pausing ProtocolHandler ["http-nio-8280"]
09-Jul-2019 22:11:57.469 INFO [main] org.apache.coyote.AbstractProtocol.pause
Pausing ProtocolHandler ["http-nio-8281"]
09-Jul-2019 22:11:57.521 INFO [main]
org.apache.catalina.core.StandardService.stopInternal Stopping service
[Catalina]
destroying LongInitServlet

shell output
$ time (bin/startup.sh ; ant -f anted-jmx/project.xml buildAndStop)
Using CATALINA_BASE:   /home/eadell/tests/apache-tomcat
Using CATALINA_HOME:   /home/eadell/tests/apache-tomcat
Using CATALINA_TMPDIR: /home/eadell/tests/apache-tomcat/temp
Using JRE_HOME:        /usr/local/java/1.9
Using CLASSPATH:      
/home/eadell/tests/apache-tomcat/bin/bootstrap.jar:/home/eadell/tests/apache-tomcat/bin/tomcat-juli.jar
Tomcat started.
Buildfile: /home/eadell/tests/apache-tomcat-8.5.15/anted-jmx/project.xml

waitMBEAN:
     [echo] Server url alive

shutdown:
     [echo] shutting down ${tomcat.catalina_base}

buildAndStop:

BUILD SUCCESSFUL
Total time: 1 minute 3 seconds

real    1m4.673s
user    0m5.157s
sys     0m0.600s


Here are the ANT targets :

<target name="waitMBEAN">
  <jmxOpen host="${jmx.server.name}" port="${jmx.server.port}"
username="controlRole" password="******" />
  <waitfor maxwait="1200" maxwaitunit="second" timeoutproperty="server.timeout"
>
      <jmxCondition
        operation="=="
        name="Catalina:type=Connector,port=8281"
        attribute="stateName" value="STARTED"
      />
  </waitfor>
  <fail if="server.timeout" message="Server url don't answer inside 1200 sec"
/>
  <echo message="Tomcat finished starting" />
</target>

<target name="shutdown" description="stop tomcat">
    <echo message="shutting down ${tomcat.catalina_base}" />
    <exec executable="/bin/bash">
        <arg line="${catalina.home}/bin/shutdown.sh" />
    </exec>
</target>

<target name="buildAndStop" depends="waitMBEAN,shutdown" />

If required you could also add targets to call servlets, and stop once you have
finished these calls.

Of course, remember to use a random JMX password then you would not compromise
all of your Tomcats if something bad happened.

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