Monday, 5 December 2016

Composing the Infinispan Docker image


In the previous post we showed how to manipulate the Infinispan Docker container configuration at both runtime and boot time.

Before diving into multi-host Docker usage, in this post we'll explore how to create multi-container Docker applications involving Infinispan with the help of Docker Compose.

For this we'll look at a typical scenario of an Infinispan server backed by an Oracle database as a cache store.

All the code for this sample can be found on github.

 

Infinispan with Oracle JDBC cache store

 


In order to have a cache with persistence with Oracle, we need to do some configuration: configure the driver in the server, create the data source associated with the driver, and configure the cache itself with JDBC persistence.

Let's take a look at each of those steps:

Obtaining and configuring the driver

The driver (ojdbc6.jar) should be downloaded and placed in the 'driver' folder of the sample project.

The module.xml declaration used to make it available on the server is as follows:


Configuring the Data source

The data source is configured in the "datasource" element of the server configuration file as shown below:


and inside the "datasource/drivers" element, we need to declare the driver:


Creating the cache

The last piece is to define a cache with the proper JDBC Store:


Putting all together

From now on, without using Docker we'd be ready to download and install Oracle following the specific instructions for your OS, then download the Infinispan Server, edit the configuration files, copy over the driver jar, figure out how to launch the database and server, taking care not to have any port conflicts.

If it sounds too much work, it's because it really is. Wouldn't it be nice to have all these wired together and launched with a simple command line? Let's take a look at the Docker way next.


 

Enter Docker Compose


Docker Compose is a tool part of the Docker stack to facilitate configuration, execution and management of related Docker containers.

By describing the application aspects in a single yaml file, it allows centralized control of the containers, including custom configuration and parameters, and it also allows runtime interactions with each of the exposed services.

Composing Infinispan

Our Docker Compose file to assemble the application is given below:

It contains two services:
  • one called oracle that uses the wnameless/oracle-xe-11g Docker image, with an environment variable to allow remote connections.
  •  another one called infinispan that uses version 8.2.5.Final of the Infinispan Server image. It is launched with a custom command pointing to the changed configuration file and it also mounts two volumes in the container: one for the driver and its module.xml and another for the folder holding our server xml configuration.

Launching

To start the application, just execute


To inspect the status of the containers:


To follow the Infinispan server logs, use:


Infinispan usually starts faster than the database, and since the server waits until the database is ready (more on that later), keep an eye in the log output for "Infinispan Server 8.2.5.Final (WildFly Core 2.0.10.Final) started". After that, both Infinispan and Oracle are properly initialized.

Testing it

Let's insert a value using the Rest endpoint from Infinispan and verify it was saved to the Oracle database:


To check the Oracle database, we can attach to the container and use Sqlplus:


Other operations


It's also possible to increase and decrease the number of containers for each of the services:



A thing or two about startup order

 

When dealing with dependent containers in Docker based environments, it's highly recommended to make the connection obtention between parties robust enough so that the fact that one dependency is not totally initialized doesn't cause the whole application to fail when starting.

Although Compose does have a depends_on instruction, it simply starts the containers in the declared order but it has no means to detected when a certain container is fully initialized and ready to serve requests before launching a dependent one.

One may be tempted to simply write some glue script to detect if a certain port is open, but that does not work in practice: the network socket may be opened, but the background service could still be in transient initialization state.

The recommended solution for this it to make whoever depends on a service to retry periodically until the dependency is ready. On the Infinispan + Oracle case, we specifically configured the data source with retries to avoid failing at once if the database is not ready:

When starting the application via Compose you'll notice that Infinispan print some WARN with connection exceptions until Oracle is available: don't panic, this is expected!


Conclusion


Docker Compose is a powerful and easy to use tool to launch applications involving multiple containers: in this post it allowed to start Infinispan plus Oracle with custom configurations with a single command.
It's also a handy tool to have during development and testing phase of a project, specially when using/evaluating Infinispan with its many possible integrations.

Be sure to check other examples of using Docker Compose involving Infinispan: the Infinispan+Spark Twitter demo, and the Infinispan+Apache Flink demo.


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