Does the Node.js agent affect my application's performance?

Question

Does the Node.js agent affect my application's performance?

Answer

As you might expect, Contrast's analysis does make your app run a little slower. The good news is it's generally not enough for anyone to complain about, and the results are definitely worth it.

Startup Time

When you start your server with Contrast, you'll notice a delay in startup time. This is first caused by the agent attempting to establish a connection with the Contrast application. High latency between the server and the Contrast application, or a Contrast application which is under heavy load, may exacerbate the startup time. Where startup time is critical, this cost can be reduced as follows:

• Run Contrast with --agent.auto_update.enable false. This will prevent the agent from checking for updates during its initial communication with the Contrast application.
• Run Contrast with --inventory.analyze_libraries false. The agent will not collect information about the application's dependencies.

For most applications, the bulk of the startup time the agents adds is caused by the source code rewrites it performs for instrumentation. This delay scales directly with the amount of source code in the application - dependencies included. Where startup time is critical, this cost can be reduced by running Contrast with --agent.node.enable_rewrite false. This option is a last resort and should be avoided, as it will drastically reduce the accuracy of our dataflow.

Request Processing Time

It's probably more important to think about how Contrast affects the round-trip time. In typical applications, Contrast may noticeably impact the round-trip time of requests that contain a lot of business logic. Round-trip times for static resources typically don't get measurably worse. In requests where the total round-trip time is dominated by database or Web Service calls, Contrast's effect will be less noticeable.

If better performance is really important to your environment, consider the following options:

• Run Contrast nightly during integration tests
• Run Contrast in an alternate environment (QA system or DEV environment)
• Run Contrast on a single node in a load-balanced environment

Dead-zoning

While it's normal to experience some overhead from our Assess instrumentation, it should not affect performance to the extent that the application is rendered unusable.  If such a performance impact is experienced, it may indicate that the agent is monitoring too many calls that it doesn't need to.

For example, the agent may try to observe too many function calls in intentionally slow operations such as the bcrypt hashing function, and the overhead this causes can cause the application to become very slow to respond.

The agent has built-in measures to avoid these situations as much as possible. To handle them, the agent employs something we call dead-zoning.  Dead-zoning disables instrumentation during operations which are too expensive to follow in detail, or which the agent does not need to watch because it provides no benefit.

For example, if we detect that our instrumentation in a library such as bcrypt-js is responsible for this kind of performance degradation, we will add it to our list of dead-zones.

If you suspect something like this is causing performance issues in your application, you can add a dead-zone for a library with the --agent.node.unsafe.deadzones option, which accepts a comma-separated list of the modules you wish to dead-zone.

If use of this setting this resolves a performance issue, please reach our to our Support team, especially if the module is a public one available in npm.  We can use this information to update our internal dead-zoning policy and improve the way we detect modules which should be dead-zoned automatically.

More Information

For additional detail on how to make any of the configuration changes documented above, please visit Node.js Agent Configuration.