tomcat-confd

This is a starting point for running and administrating multiple Apache Tomcat using a central Configuration Repository - here etcd.

The main subject under test&sample is confd. It is a tiny useful tool to move distributed local configuration files to a central configuration repositories. Various other configuration repositories like etcd, redis, consul, dynamodb, zookeeper could be used instead of etcd if required.

Here we use Apache httpd as a reverse proxy for load balancing. Why? It is since 1996 the most popular WebServer and it works fine :)

Feel free to compare this confd sample with my tomcat-consul sample.

what is this sample doing?

Apache Tomcat uses config files e.g. tomcat-users.xml to define access rights to the manager webapp or server.xml to define connectors. Here the admin credentials shall be configured centrally, so we can change them within etcd.

The full list of confd responsible configurations - all of them stored in etcd under the prefix 'tomcat':

• Xmx: maximum heap size
• Xms: initial heap size
• username: manager webapp username
• password: manager webapp password
• maxThreads: count of threads for a connector
• jvmRoute: here Tomcat hostname (as defined in docker-compose.yml)

Apache httpd is forwarding requests via mod_proxy_ajp to the Tomcats. To register all running Containers gliderlabs/registrator will be used.

run it

This sample uses Vagrant and VMware or VirtualBox. Vagrant is optional - you can build and run the Containers via docker-compose.yml also directly in your prefered Docker environment. A Docker-Compose file exists for that.

run it via Vagrant

vagrant plugin list
vagrant plugin install vagrant-docker-compose

Clone this repo, run it

git clone https://github.com/muenchhausen/tomcat-confd.git
cd tomcat-confd
vagrant up

Find out the IP of your VM - e.g. login into the VM (sometimes credentials vagrant vagrant are required)

vagrant ssh
ifconfig

run it directly with Docker Compose

cd tomcat-confd/docker
docker-compose build
docker-compose up

try Tomcat in your Browser

Open your Browser, go to Tomcat Manager http://192.168.99.100:8081/manager/ login with credentials admin and admin

try also second Tomcat Manager http://192.168.99.100:8082/manager/ login with same credentials as above

try etcd in your Browser

Look to your Tomcat keys and Values: http://192.168.99.100:2379/v2/keys/tomcat/

Look what gliderlabs/registrator added: http://192.168.99.100:2379/v2/keys/docker-services/

try Apache httpd reverse proxy in your Browser

Look to Apache server-status: http://192.168.99.100/server-status/

Access the Tomcat default Sample over httpd: http://192.168.99.100/examples/servlets/servlet/SessionExample You will see that the session id alternates if you refresh the browser

CoreOS Meetup Munich 2016-03-03

here are the slides and the presentation

some interesting code snippets

Besides the automatic vagrant up way, you can play around with manual steps. Here some ideas...

manually rebuild everything within the VM

sudo su -
cd /vagrant/docker
docker-compose stop && docker-compose rm -f && docker-compose build && docker-compose up --force-recreate

open another bash - fill in the required etcd keys - after doing this tomcat should start

if using vagrant:

curl -L http://localhost:2379/v2/keys/tomcat/Xmx -XPUT -d value='1024M' && \
curl -L http://localhost:2379/v2/keys/tomcat/Xms -XPUT -d value='512M' && \
curl -L http://localhost:2379/v2/keys/tomcat/user -XPUT -d value='admin' && \
curl -L http://localhost:2379/v2/keys/tomcat/password -XPUT -d value='admin' && \
curl -L http://localhost:2379/v2/keys/tomcat/maxThreads -XPUT -d value='123'

if using docker tools - find out ip with docker-machine env then run e.g.

curl -L http://192.168.99.100:2379/v2/keys/tomcat/Xmx -XPUT -d value='1024M' && \
curl -L http://192.168.99.100:2379/v2/keys/tomcat/Xms -XPUT -d value='512M' && \
curl -L http://192.168.99.100:2379/v2/keys/tomcat/user -XPUT -d value='admin' && \
curl -L http://192.168.99.100:2379/v2/keys/tomcat/password -XPUT -d value='admin' && \
curl -L http://192.168.99.100:2379/v2/keys/tomcat/maxThreads -XPUT -d value='123'

debug confd - e.g. test if templates are ok

/usr/local/bin/confd -onetime -backend etcd -node docker_etcdservice_1:4001

open issues - what's next?

• try latest confd version v0.12 and define default values getv within template files.
• how to handle consistent configuration changes with confd
• confd for Windows :)