Disabling Hystrix on the Store server

In HCL Commerce, the Commerce Remote Store (CRS), otherwise known as the Store server, implements the Hystrix framework as a proxy for backend resources such as the Transaction server and Search server by default. This can be disabled, but does have performance implications that must be considered.

About this task

The Hystrix framework executes back-end requests on a separate thread pool to help control and limit the number of concurrent threads that are allowed. The framework also provides other features such as circuit breakers, timeouts, fall backs, and metrics, but these capabilities are not used with the CRS.

Impacts on HCL Commerce include increased troubleshooting complexity and higher memory requirements. Another consideration that must be made is the fact that Hystrix is no longer maintained to a high degree. These factors must be weighed against its limited use by the CRS. Taking these factors into consideration, it is recommended that this feature be disabled.

Procedure

Disable Hystrix on the Store server.
1. Open the Store server configuration file (wc-store.xml) for editing.
  This file is located within the crs.ear/xml/config/ directory.
2. Set the enableHystrix parameter to false.
  The following can be added to your Dockerfile to implement this change on image deployment.
```
RUN sed -i 's/enableHystrix=\"true\"/enableHystrix=\"false\"/g' /opt/WebSphere/Liberty/usr/servers/default/apps/crs.ear/xml/config/wc-store.xml
```
Reconfiguring the Default Executor thread pool.

The WebSphere Application Server Liberty server that the CRS runs on implements a single thread pool named "Default Executor" to handle incoming requests. This pool is self-tuned and adapts to the current workload by dynamically adding or removing threads.

The implication of disabling the Hystrix request pools is that in case of a slow down in the back-end servers WebSphere Application Server Liberty might allow the Default Executor pool to expand, which could result in a large number of threads executing and waiting for a response from the back-end services. To avoid this condition, it is possible to configure the Default Executor pool with an upper limit by adding a custom configuration file.

To set a limit for the Default Executor pool, customize the CRS image by adding a new WebSphere Application Server Liberty configuration file.
1. Create a file named threadpool.xml.
  Within it, add the following configuration:
```
<server>
    <executor name="Default Executor" id="default" coreThreads="50" maxThreads="50" />
</server>
```
2. Add the threadpool.xml configuration file to the CRS image by adding this instruction to Dockerfile.
```
COPY threadpool.xml /opt/WebSphere/Liberty/usr/servers/default/configDropins/overrides/threadpool.xml
```

Results

Hystrix is no longer used to proxy requests to the back-end services. The Default Executor pool is constrained to avoid the possibility of unbounded threads waiting and causing performance implications.