(For more resources related to this topic, see here.)

Platform as a Service is a very interesting take on the traditional cloud computing models. While there are many (often conflicting) definitions of a PaaS, for all practical purposes, PaaS provides a complete platform and environment to build and host applications or services. Emphasis is clearly on providing an end-to-end precreated environment to develop and deploy the application that automatically scales as required. PaaS packs together all the necessary components such as an operating system, database, programming language, libraries, web or application container, and a storage or hosting option. PaaS offerings vary and their chargebacks are dependent on what is utilized by the end user. There are excellent public offerings of PaaS such as Google App Engine, Heroku, Microsoft Azure, and Amazon Elastic Beanstalk. In a private cloud offering for an enterprise, it is possible to implement a similar PaaS environment. Out of the various possibilities, we will focus on building a Database as a Service (DBaaS) infrastructure using Oracle Enterprise Manager. DBaaS is sometimes seen as a mix of PaaS or SaaS depending on the kind of service it provides. DBaaS that provides services such as a database would be leaning more towards its PaaS legacy; but if it provides a service such as Business Intelligence, it takes more of a SaaS form.

Oracle Enterprise Manager enables self-service provisioning of virtualized database instances out of a common shared database instance or cluster. Oracle Database is built to be clustered, and this makes it an easy fit for a robust DBaaS platform.

Setting up the PaaS infrastructure

Before we go about implementing a DBaaS, we will need to make sure our common platform is up and working.

We will now check how we can create a PaaS Zone.

Creating a PaaS Zone

Enterprise Manager groups host or Oracle VM Manager Zones into PaaS Infrastructure Zones. You will need to have at least one PaaS Zone before you can add more features into the setup. To create a PaaS Zone, make sure that you have the following:

The EM_CLOUD_ADMINISTRATOR, EM_SSA_ADMINISTRATOR, and EM_SSA_USER roles created
A software library

To set up a PaaS Infrastructure Zone, perform the following steps:

Navigate to Setup | Cloud | PaaS Infrastructure Zone.
Click on Create in the PaaS Infrastructure Zone main page.
Enter the necessary details for PaaS Infrastructure Zone such as Name and Description.
Based on the type of members you want to add to this zone, you can select any of the following member types:
- Host: This option will only allow the host targets to be part of this zone. Also, make sure you provide the necessary details for the placement policy constraints defined per host. These values are used to prevent over utilization of hosts which are already being heavily used.
  You can set a percentage threshold for Maximum CPU Utilization and Maximum Memory Allocation. Any host exceeding this threshold will not be used for provisioning.
- OVM Zone: This option will allow you to add Oracle Virtual Manager Zone targets:
  
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If you select Host at this stage, you will see the following page:
Click on the + button to add named credentials and make sure you click on Test Credentials button to verify the credential. These named credentials must be global and available on all the hosts in this zone.
Click on the Add button to add target hosts to this zone.
If you selected OVM Zone in the previous screen (step 1 of 4), you will be presented with the following screen:
Click on the Add button to add roles that can access this PaaS Infrastructure Zone.

Once you have created a PaaS Infrastructure Zone, you can proceed with setting up necessary pieces for a DBaaS. However, time and again you might want to edit or review your PaaS Infrastructure Zone.

To view and manage your PaaS Infrastructure Zones, navigate to Enterprise Menu | Cloud | Middleware and Database Cloud | PaaS Infrastructure Zones.
From this page you can create, edit, delete, or view more details for a PaaS Infrastructure Zone. Clicking on the PaaS infrastructure zone link will display a detailed drill-down page with quite a few details related to that zone. The page is shown as follows:

This page shows a lot of very useful details about the zone. Some of them are listed as follows:

General: This section shows stats for this zone and shows details such as the total number of software pools, Oracle VM zones, member types (hosts or Oracle VM Zones), and other related details.
CPU and Memory: This section gives an overview of CPU and memory utilization across all servers in the zone.
Issues: This section shows incidents and problems for the target. This is a handy summary to check if there are any issues that needs attention.
Request Summary: This section shows the status of requests being processed currently.
Software Pool Summary: This section shows the name and type of each software pool in the zone.
Unallocated Servers: This section shows a list of servers that are not associated with any software pool.
Members: This section shows the members of the zones and the member.
Service Template Summary: Shows the service templates associated with the zone.