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Apache Tomcat is an open source implementation of the Java Servlet and JavaServer Pages (JSP) specifications, and provides a "pure Java" HTTP web server environment for Java web applications to run.
Apache Tomcat 7 implements the Java Servlet 3.0 and JSP 2.0 specification from Sun Microsystems/Oracle.
http://tomcat.apache.org
A tomcat deployment consists of a Tomcat service:
juju deploy tomcat
By default, this is Tomcat version 7. You can deploy Tomcat 6 by specifying the version at deployment. First create a YAML file with the contents:
tomcat: tomcat_version: tomcat6
Then deploy:
juju deploy --config config.yaml tomcat
Once deployed, you can specify what http port to use:
# use port 80 for http juju set tomcat http_port=80
(NOTE: You could also do this at deployment with the --config switch)
--config
The Tomcat manager applications, enabled by default, are protected by HTTP basic password protection. To access the applications you must set a password for either the admin or status roles. The admin role has full access to configure Tomcat whereas the status role may only see server status. To set passwords:
admin
status
juju set tomcat admin_password=<password> juju set tomcat status_password=<password>
To expose Tomcat to the Internet:
juju expose tomcat Open web browser to http://<host>/manager or http://<host>/manager/status using your admin or status username/password respectively.
(Note: Passwords will be sent to the manager in plain text, so it is recommended to enable HTTPS as follows)
To enable HTTPS:
# enable https connector juju set tomcat https_enabled=True # use port 443 for https juju set tomcat https_port=443 Open web browser to https://<host>/manager or https://<host>/manager/status.
A self-signed certificate will be generated for HTTPS use by default. You can specify your own private key and certificate as a PKCS12 file as follows:
# set pkcs12 file juju set tomcat keystore=`base64 < <pkcs12 file>` # set pkcs12 file password juju set tomcat keystore_password=<password>
The PKCS12 file is transmitted securely to your Juju cluster and subsequently used by all service units (added with juju add-unit) for easy certificate management. Should you remove your certificate by setting keystore to an empty string, a new self-signed certificate will be generated for use.
juju add-unit
keystore
While the manager applications are a useful way of testing a Tomcat installation there is no real usage for them when deploying applications using a Juju subordinate charm like j2ee-deployer. Therefore as a security precaution, it is recommended you disable them in a production environment:
j2ee-deployer
# disable manager applications juju set tomcat manager_enabled=False
Tomcat offers two pure Java HTTP connectors, Blocking I/O ("bio") and Non-Blocking I/O ("nio").
If you have enough traffic to be concerned about performance of each, it is recommended you benchmark both. Better performance can be achieved with either depending on conditions. Traditionally, Java application traffic favors the bio connector and serving of static content with the nio connector.
You may set either as follows:
# set nio connector juju set tomcat http_connector=nio # set bio connector juju set tomcat http_connector=bio
A webapp can be deployed with the Tomcat charm in one of two ways: it can be provided by another charm, or you can manually upload it.
For another charm to provide a webapp, it must be a subordinate charm that supports the java-webapp relation.
java-webapp
To upload a webapp to Tomcat, simply use the following:
juju scp webapp.war tomcat/0: juju ssh tomcat/0 'sudo mv webapp.war /var/lib/tomcat7/webapps'
(If you changed the version of tomcat being deployed, you will need to adjust the path appropriately.)
Remote debugging can be useful for application development and diagnosing problems with a deployed application. There are many debugging tools, including jdb, and most Integrated Development Environments (IDEs) provide the ability to attach to remote servers and step through code line by line. The tomcat charm provides the ability to attach remote debuggers by using the debug_enabled configuration option. The default port 8000 is open when True and closed when False (default).
debug_enabled
True
False
JMX monitoring is disabled by default, but you can enable it with the following commands:
juju set tomcat jmx_enabled=True juju set tomcat jmx_control_password=<password> juju set tomcat jmx_monitor_password=<password>
The control role (username = controlRole) allows read/write access, the monitor role (username = monitorRole) read only access. If a password is empty, it disables access for that role.
controlRole
monitorRole
There is a further JMX option, jmx_localhost. This determines what hostname is given to the JMX client to connect to. If false, the internal hostname or private IP address of the unit will be used, meaning connection is suited to either LXC based deployments or cloud deployments where you have VPN access:
jmx_localhost
JConsole or VisualVM connect to <private unit address>:10001 with username/password
For cloud deployments, setting this to True uses hostname localhost, which allows you to connect over a ssh tunnel:
localhost
ssh -L 10001:localhost:10001 -L 10002:localhost:10002 <public unit address> JConsole or VisualVM connect to localhost:10001 with username/password
The latter is much more typical of out of the box deployment, so jmx-localhost defaults to True.
jmx-localhost
Tomcat supports adding arbitrary configuration parameters for JNDI lookup by deployed applications. This enables you to develop applications that discover configuration details at runtime simply by referencing pre-determined JNDI names. This charm supports lookup of different Juju services, each of which may be configured using the appropriate jndi_<type>_config option. Unless specified otherwise, options are generally a comma separated list of JNDI name, service and type specific colon separated values:
jndi_<type>_config
<name>:<service>,<name>:<service>
This allows you to map Juju services to JNDI names as follows:
# map the JNDI name 'param/Memcached' to the Juju service named 'memcached' juju set tomcat jndi_memcached_config="param/Memcached:memcached" # map the JNDI name 'param/Terracotta' to the Juju service named 'terracotta' juju set tomcat jndi_terracotta_config="param/Terracotta:terracotta"
The charm will take care of mapping the JNDI name with the private addresses of the Juju services. If you add units of memcached or terracotta the charm will add the new addresses appropriately. A brief description of the available JNDI relations is below.
Memcached (jndi_memcached_config) - Provides a space separated string of all unit addresses for specified memcached service. This can be used directly in instantiating an instance of a Memcached client such as spymemcached (see http://code.google.com/p/spymemcached/ for more details).
jndi_memcached_config
Terracotta (jndi_terracotta_config) - Provides a comma separated string of all unit addresses for the specified Terracotta service. This can be injected directly into EHCache or Quartz configuration (see http://www.terracotta.org for more details).
jndi_terracotta_config
Tomcat supports session clustering, allowing a group of Tomcat units to replicate J2EE session information to each other. This is useful for HA deployments where session contents are important. To enable clustering across units:
# enable clustering juju set tomcat cluster_enabled=True # add 2 more units to cluster juju add-unit -n 2 tomcat
By default, static membership is used over multicast based membership which means units depend on local cluster configuration to determine cluster groups. Multicast uses multicast UDP packets on a pre-determined address/port to determine cluster groups. Where a cloud provider such as EC2 disables multicast traffic between instances, static membership must be used. Where multicast traffic is allowed, it is preferred and may be enabled as follows:
# enable multicast clustering juju set tomcat multicast=True # set multicast address juju set tomcat multicast_address=228.0.0.4 # set multicast port juju set tomcat multicast_port=34569
For maximum performance with clustering, it is recommended you use a load balancer in front of Tomcat that supports "sticky sessions".
This charm was originally written by Robert Ayres robert.ayres@ubuntu.com and is maintained by Matthew Bruzek matthew.bruzek@canonical.com. If you encounter a bug with the tomcat charm please open a bug.