tomcat

How to use Tomcat on DC/OS

Apache Tomcat provides implementations of Servlet, JSP, EL and WebSocket from the Java EE Web Application Container specification.

• Estimated time for completion: 10 minutes
• Target audience: Anyone interested in using a Java app server.
• Scope: Learn to install and run Tomcat.

Table of Contents:

• Prerequisites
• Launch Tomcat
• Access Tomcat
• Shut down Tomcat

Prerequisites

• A running DC/OS 1.8 cluster with at least 1 public agent node.
• DC/OS CLI installed.
• jq installed.
• SSH configured.

Launch Tomcat

Download the provided Marathon app spec for Tomcat, tomcat.json, to your local machine where the DC/OS CLI is installed:

$ curl -O https://raw.githubusercontent.com/dcos/examples/master/1.8/tomcat/tomcat.json

Lets inspect the tomcat.json file:

{
  "id": "/tomcat",
  "instances": 1,
  "cpus": 1,
  "mem": 512,
  "container": {
    "type": "DOCKER",
    "docker": {
      "image": "tomcat:8.5",
      "network": "BRIDGE",
      "portMappings": [
        {
          "protocol": "tcp",
          "hostPort": 80,
          "containerPort": 8080
        }
      ]
    }
  },
  "requirePorts": true,
  "acceptedResourceRoles": [
    "slave_public"
  ],
  "env": {
    "JAVA_OPTS": "-Xms256m -Xmx256m"
  },
  "healthChecks": [
    {
      "gracePeriodSeconds": 120,
      "intervalSeconds": 30,
      "maxConsecutiveFailures": 3,
      "path": "/",
      "portIndex": 0,
      "protocol": "HTTP",
      "timeoutSeconds": 5
    }
  ]
}

Here we've defined the app (.id) to be /tomcat. We want Marathon to run one instance of Tomcat for us on our cluster, each instance will require one cpu share (.cpus), 512 MB of RAM (.mem) and port 80 (.container.docker.portMappings[0].hostPort). We then tell Marathon the container image we want Tomcat to be ran from, in this case we're running tomcat:8.5 from DockerHub (.container.docker.image).

We've specified that Marathon should run the Docker image using Bridge Networking (.container.docker.network), and specified that TCP port 80 on the host (.container.docker.portMappings[0].hostPort) should be forwarded to TCP port 8080 inside the container (.container.docker.portMappings[0].containerPort). Further, we tell Marathon that we have to run on port 80 by setting .requirePorts to true.

To ensure that we can get to Tomcat on the internet we instruct Marathon to only run Tomcat on a node that has the role slave_public (which is the public agent node).

Next we define the JAVA_OPTS that Tomcat will start with (.env.JAVA_OPTS). Finally we define a health check for Tomcat, Marathon will use this health check to automatically restart our container if Tomcat becomes unhealthy or unresponsive.

Now we can run the service through submitting the above app spec tomcat.json to Marathon:

$ dcos marathon app add tomcat.json

To validate that that Tomcat is running, do the following:

$ dcos marathon app list
ID       MEM  CPUS  TASKS  HEALTH  DEPLOYMENT  CONTAINER  CMD
/tomcat  512   1     1/1    1/1       ---        DOCKER   None

Access Tomcat

To access Tomcat, navigate to the public agent, that is, http://<public_agent_public_ip> and note that you'll need to find the IP of the public agent first, for this to work.

In this example the public IP address is 52.51.80.141 and when we navigate there, we see something like the following:

View task logs in DC/OS UI

From the Services tab of the DC/OS UI you can click on tomcat to see the list of tasks running:

Click on the Logs tab to see the following:

View task logs via DC/OS CLI

Run this command to tail the stderr file of Tomcat via the DC/OS CLI:

$ dcos task log --follow tomcat stderr
02-Nov-2016 15:56:00.598 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deployment of web application directory /usr/local/tomcat/webapps/host-manager has finished in 42 ms
02-Nov-2016 15:56:00.599 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deploying web application directory /usr/local/tomcat/webapps/ROOT
02-Nov-2016 15:56:00.617 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deployment of web application directory /usr/local/tomcat/webapps/ROOT has finished in 17 ms
02-Nov-2016 15:56:00.617 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deploying web application directory /usr/local/tomcat/webapps/examples
02-Nov-2016 15:56:01.036 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deployment of web application directory /usr/local/tomcat/webapps/examples has finished in 419 ms
02-Nov-2016 15:56:01.037 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deploying web application directory /usr/local/tomcat/webapps/docs
02-Nov-2016 15:56:01.054 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deployment of web application directory /usr/local/tomcat/webapps/docs has finished in 18 ms
02-Nov-2016 15:56:01.058 INFO [main] org.apache.coyote.AbstractProtocol.start Starting ProtocolHandler [http-nio-8080]
02-Nov-2016 15:56:01.064 INFO [main] org.apache.coyote.AbstractProtocol.start Starting ProtocolHandler [ajp-nio-8009]
02-Nov-2016 15:56:01.066 INFO [main] org.apache.catalina.startup.Catalina.start Server startup in 921 ms

Shut down Tomcat

To shut down and remove Tomcat, do:

$ dcos marathon app remove /tomcat

Note that the log files generated when running Tomcat will be automatically cleaned up by DC/OS.