WSO2 Patch Application Process

You apply patches to WSO2 products either as individual patches or through a service pack. A service pack is recommended when the number of patches increase. The following sections explain the WSO2 patch application process:

Before you begin

You can download all WSO2 Carbon Kernel patches from here.
Before you apply a patch, check its README.txt file for any configuration changes required.

Applying service packs to the product

From version 4.2.0 onwards, Carbon Kernel supports service packs. A service pack is a collection of patches in a single pack. It contains two elements:

The lib directory: contains all the JARs relevant to the service pack.
The servicepack_patches.txt text file: contains the list of JARs in the service pack.

Follow the steps below to apply service packs to your product.

Copy the service pack file to the <PRODUCT_HOME>/repository/components/servicepacks/ directory. For example, the image below shows how a new service pack named servicepack001 is added to this directory.
Start your product. The following steps will be executed:
1. Before applying any patches, the process first creates a backup folder named patch0000 inside the <PRODUCT_HOME>/repository/components/patches/ directory, which will contain the original content of the <PRODUCT_HOME>/repository/components/plugins/ directory. This step enables you to revert back to the previous state if something goes wrong during operations.
2. The latest service pack in the <PRODUCT_HOME>/repository/components/servicepacks/ directory will be applied. That is, the patches in the service pack will be applied to the <PRODUCT_HOME>/repository/components/plugins/ directory.
3. In addition to the service pack, if there are individual patches added to the <PRODUCT_HOME>/repository/components/patches/ directory, those will also be incrementally applied to the plugins directory.
  
  The metadata file available in the service pack will maintain a list of the applied patches by service pack. Therefore, the metadata file information will be compared against the <PRODUCT_HOME>/repository/components/patches/ directory, and only the patches that were not applied by the service pack will be incrementally applied to the plugins directory.

Applying individual patches to the product

You can apply each patch individually to your system as explained below. Alternatively, you can apply patches through service packs as explained above.

Copy the patches to the <PRODUCT_HOME>/repository/components/patches/ directory.
Start the Carbon server. The patches will then be incrementally applied to the plugins directory.

Before applying any patches, the process first creates a backup folder named patch0000 inside the <PRODUCT_HOME>/repository/components/patches/ directory, which will contain the original content of the <PRODUCT_HOME>/repository/components/plugins/ directory. This step enables you to revert back to the previous state if something goes wrong during operations.

Prior to Carbon 4.2.0, users were expected to apply patches by starting the server with wso2server.sh -DapplyPatches. Now, you do not have to issue a special command to trigger the patch application process. It starts automatically if there are changes in either the <PRODUCT_HOME>/repository/components/servicepacks/ directory or the <PRODUCT_HOME>/repository/components/patches/ directory. It verifies all the latest JARs in the servicepacks and patches directories against the JARs in the plugins directory by comparing MD5s of JARs.

Verifying the patch application

After the patch application process is completed, the patch verification process ensures that the latest service pack and other existing patches are correctly applied to the <PRODUCT_HOME>/repository/components/plugins/ folder.

All patch related logs are recorded in the <PRODUCT_HOME>/repository/logs/patches.log file.
The <PRODUCT_HOME>/repository/components/patches/.metadata/prePatchedJARs.txt meta file contains the list of patched JARs and the md5 values.
A list of all the applied service packs and patches are in the <PRODUCT_HOME>/repository/components/default/configuration/prePatched.txt file.

Do not change the data in the <PRODUCT_HOME>/repository/components/default/configuration/prePatched.txt file. The patch application process gets the pre-patched list from this file and compares the list with the patches available in the servicepack and patches directories. If you change the data in this file, you will get a startup error when applying patches.

Overview of the patch application process

The diagram below shows how the patch application process is implemented when you start the server.
Flow chart of patch application process. After server startup, if there are service packs or patch changes, they are applied. Next, MD5 verification is performed on the latest patched JARs against the JARs in plugin. Any warnings during this process are logged.