Analyzing logs is critical so you can understand application behavior and identify potential issues. However, an overwhelming amount of logs can make it challenging to find relevant information. To tackle this, you can break logs into individual fields and remove unnecessary attributes using appropriate log-matching techniques and drop filters. Then you can focus on critical data and gain valuable insights quickly. This blog will explore common techniques, highlight available resources, and offer practical suggestions on using drop filters to help you maximize the potential of New Relic.

Regular expressions for logs

Regular expressions (regex) are powerful tools for finding and matching text data patterns. They are commonly used in log analysis to filter records based on specific patterns or expressions, which makes finding and analyzing relevant data easier. A regex pattern is constructed using a combination of characters that match a specific set or range of characters.

Here is an example where the following regular expression is used to verify credit card numbers that start with a four and have a length of 13-16 digits:


Here's a breakdown of the regex:

  • ^ indicates the start of the string.
  • 4 matches the first digit of the credit card number.
  • [0-9]{12} matches 12 digits from 0-9 following the first digit 4.
  • (?:[0-9]{3})? matches an optional group of 3 digits from 0-9 at the end of the string.
  • $ indicates the end of the string.

These patterns can be customized to match the exact text you're looking for in a log file, making it easier to identify relevant information and discard irrelevant data. 

It's important to note that the pattern attribute in New Relic infrastructure works similarly to the grep -E command in Unix systems—it is only supported for tail, systemd, syslog, and tcp (only with format none) sources. The grep -E command is used in Linux and Unix systems to search for specific text or strings within a file. It explores the specified file for lines that match the selected words or strings.

Here is an example of a regular expression as seen in the New Relic docs to filter for records containing either WARN or ERROR:

- name: only WARN or ERROR
 file: /var/log/logFile.log
 pattern: WARN|ERROR

Here is another example of using a regular expression to filter NGINX containing either 400, 404, or 500:

 - name: nginx
   file: /var/log/nginx.log
     logtype: nginx
     environment: production
     engineer: yourname
   pattern: 500|404|400

For more information, read the docs on the pattern attribute with New Relic infrastructure.

Mastering regex can help you gain valuable insights into your application and infrastructure performance. This can help you troubleshoot issues and make data-driven decisions to improve your overall system health. 

In the next section, you will learn about client and server-side log filtering with New Relic.

Client-side log filtering using the pattern attribute

You can use regular expressions (regex) with New Relic logs to quickly and effectively filter through large volumes of log data. Here is an example of how to use the pattern attribute in the context of New Relic infrastructure:

Step 1: Get started with New Relic infrastructure monitoring

You need to first install the New Relic infrastructure agent successfully and navigate to the log forwarder configuration folder. logging.d will be the main folder for all logs configuration, which you'll find in this location:

  • On Linux: /etc/newrelic-infra/logging.d/
  • On Windows: C:\Program Files\New Relic\newrelic-infra\logging.d\

Step 2: Define a log source

To configure log forwarding parameters for New Relic infrastructure monitoring, you need to include a name and log source parameter in the log forwarding .yml configuration file. Begin by defining a name for the log or logs you want to forward to New Relic. 

 - name: example-log
   file: /var/log/example.log # directory to your log path
 - name: example-log-two
   file: /var/log/example-two.log # directory to another log path

The file field is used to specify the location of the log file(s) that the agent will monitor for changes. The agent tracks the changes in the log files in a way that is similar to how the tail -f shell command works.

Step 3: Add the pattern attribute

Add the pattern attribute to your logs configuration as seen with this NGINX example.

 - name: nginx
   file: /var/log/nginx.log
     logtype: nginx
     environment: workshop
     engineer: yourname
   pattern: 500|404|400

Step 4: View the results

Once you have configured New Relic correctly and confirmed that it is collecting data, you can view your log data and related telemetry data in New Relic. See the next image for an example of the end result of applying pattern to the status codes 500, 404, or 500 on NGINX. Now only logs with those status codes are shown in New Relic and this improves the overall quality of the logs received in New Relic. 

Here is the end result after applying Pattern for 500, 404, or 500.

With these steps, you can efficiently filter through vast amounts of log data via client-side and gain valuable insights into the performance of your application and infrastructure.

Server-side log filtering using drop filters

Once log event data is sent to New Relic, it can be stored in our NRDB database or discarded. You can discard log data by creating drop filters using the logs management UI or GraphQL.

A drop filter is a special rule that matches data based on a query. When creating drop rules, make sure they accurately identify and discard data that meets your established conditions.

When triggered, the drop filter removes the matching data from the ingestion pipeline before it reaches the New Relic Database (NRDB).

For more information about drop filters, see How drop filters work in the New Relic documentation.

Diagram of dropping log data with drop filters

It's important to note that data removed by the drop filter rule cannot be queried and, once discarded, cannot be restored. Because of that, you must carefully monitoring the filter rule(s) you create and the data you send to New Relic. Here are the steps to create a drop filter from an attribute in New Relic:

Step 1: Navigate to Logs

Go to and navigate to Logs. To open the log detail view of the log that contains the attribute you want to remove, click on All Logs, and then click on an individual log.

View logs by selecting logs

Step 2: Create a drop filter

Within the log detail view, open the attribute menu by clicking on the desired attribute. For example, select auth. Then, select Create drop filter from attribute.

Creating a drop filter from an attribute

Step 3: Configure your filter

When creating a drop filter for your logs, it's important to give it a name that accurately describes what it does. The NRQL field will automatically be filled with the attribute's key and value based on your previous selection, but you can edit it if needed.

Menu for drop filter configuring

In this example, the filter is based on the filePath where the NGINX logs are received. This field specifies the location of the log file(s) that the agent will monitor for changes. The agent tracks changes in the log files similarly to the tail -f shell command. You can then choose to drop the entire log event or specific attributes from matching events. Once you've decided, save the drop filter rule to finalize the process.

Step 4: See the before and after with drop filters

After correctly configuring New Relic and confirming that data is being collected, you can view the log data with the applied drop filters. Let's see how the log data looks before and after applying drop filters.

Results before a drop filter

In the previous image, the attributes auth, ident, and referrer are recorded in New Relic before the drop filters are applied. These attributes can create unnecessary noise when dealing with many attributes or when the size of each log is huge.

The next image shows what the log details looks like after drop filters are applied.

After drop filter

Notice how the drop filters have successfully removed the  auth, ident, and referrer log attributes.

As you can see from this example, when you use drop filters, you can improve the quality of the logs received in New Relic by eliminating unnecessary information. This allows you to focus on the critical data relevant to your analysis so you can better understand the performance of your application and infrastructure.

Frequently Asked Questions

Is it possible to drop attributes programmatically?

You can drop log attributes in New Relic using the NerdGraph API. To achieve this, you must create a drop rule in NerdGraph format that contains an NRQL string to specify the data types you want to drop, and an "action" type to determine how the NRQL string is applied. The NerdGraph Explorer can help you make and test all the necessary calls. You can learn more about NerdGraph and NRQL in the New Relic documentation and the NRQL documentation, respectively.


In this blog, you learned how to improve log quality in New Relic by using the pattern attribute in New Relic infrastructure for client-side filtering, and using UI drop filters for server-side filtering to remove matching data during ingestion. These techniques allow you to remove unnecessary attributes, focus on critical log data, and maximize the potential of New Relic for log analysis.

For additional reading, check out these docs: