Active vs. Passive Monitoring: What’s The Difference?

Today, it’s perfectly normal for businesses to continuously monitor software applications and IT infrastructure to ensure uninterrupted customer service.

Active and passive monitoring are the two popular methods enterprises use for infrastructure and application performance monitoring (APM). As the names indicate, these two approaches to monitoring are very different.

This article explains the differences between active and passive monitoring methods, along with their use cases, data volumes, and control over the data. Additionally, we’ll look at the advantages and drawbacks of these two methods. 

Summary: Active vs. passive monitoring

This article is comprehensive, so to help you out, I’ve summed up the major points here. Keep reading after the table to get more details.

What is Active Monitoring?

Active monitoring refers to proactively monitoring the performance of:

• Networks
• Applications
• Infrastructure

Active monitoring will be based on the results of synthetically generated data. For example, during active network monitoring, test network packets are ingested to simulate the actual network behavior. This helps observe the measurements of various performance parameters. During the process, extra traffic is created to predict the potential performance.

Synthetic journeys are created through active monitoring of applications and services. These journeys use test accounts to mimic critical user journeys throughout the application. Active monitoring is also called ‘synthetic monitoring', as it does not use real data.

(Related reading: network monitoring, network configuration & baselining network behavior using ML.)

What is Passive Monitoring?

In contrast, passive monitoring uses real data to measure and analyze the performance of networks, applications, and infrastructure. Using special devices and software, passive monitoring provides a holistic and in-depth view of real performance.

For example, in passive network monitoring:

• Packet sniffers monitor and analyze network traffic.
• Pooling techniques periodically collect information.

Unlike active monitoring, passive monitoring uses a large volume of data and does not add additional data to the normal network flow.

(Learn about real user monitoring, aka RUM, or take a free tour of Splunk RUM.)

Active vs. Passive Monitoring: Use cases

There are several use cases for the two methods based on the nature of the data used and the analysis approach. We will discuss them next.

Active Monitoring

Active monitoring is best suited in the following scenarios, as it uses a predictive approach.

• Testing the Quality of Service (QoS) provided by networks. Enables running simulations to test if the network meets the QoS requirements of networks, such as latency and bandwidth.
• Identifying potential application issues. In application monitoring, synthetic journeys can be created using test accounts and data to run periodically. Failures of such journeys indicate a potential issue and allow time to fix before it impacts the end users.
• Evaluating the performance of new hardware resources. Before deploying the new hardware into networks, you can use active monitoring to establish performance baselines using the existing hardware for comparison. 
• Benchmarking the network performance. For example, to benchmark the CPU, memory, disk I/O, and network utilization during specific user flows.

Passive Monitoring

Passive monitoring is best suited for the following scenarios, as it uses actual data to monitor performance.

• Monitoring server and network status and health. Periodic ping results from application servers and network devices like routers and switches indicate the health and status of servers. 
• Identifying trends in customer usage. Real data feeds provide a holistic view of customer usage patterns and potential improvement areas over time. 
• Personalizing the user experience. By analyzing customer usage trends over time, companies can identify their preferences and provide personalized services.
• Alerting on issues that need immediate attention. Indicates issues that have a direct impact on end-users so that immediate action can be taken.
• Running Intrusion Detection Systems. IDSs continuously monitor the network to indicate if there is any unusual traffic pattern, which can be malware or other attempted breach

Data volume & control over data

Both methods utilize user data to continuously monitor the system under investigation. However, the data volume and the control over the data significantly differ in each method.

Active monitoring

Lower data requirements and usage. The data used in active monitoring is comparably lower than passive monitoring, as it involves specific and targeted tests during a specific period. Hence, data is more focused and related to specific performance metrics being tested, such as:

• Bandwidth
• Latency
• Throughput
• Packet loss

Thus, you can tweak the amount and various aspects of the traffic you send in. You only need a little of it to get significant measurements.

Environmental control. Another factor is that active monitoring offers more control over the generating data and the simulation environment. For example, you can determine the period of execution, if it is network monitoring, the packet size, the types, and so on.

Passive monitoring

In contrast, passive monitoring continuously captures data, producing more data for analysis. In fact, data can be collected over a 24/7 period via passive monitoring. This data can be generated from various sources, commonly:

• Sensors
• Network traffic
• Error logs

All this added data means that storage requirements are higher, and any analysis can be more complex than active monitoring. Important to remember, with passive monitoring, you’ll have less control over the generated data than active monitoring.

Advantages

Both methods bring several advantages for organizations.

Benefits of active monitoring

Helps proactively identify underlying issues. Active monitoring simulates user journeys and network behaviors continuously, even before users use the system during usage times. Therefore, it helps identify problems before they impact real users. (In contrast passive monitoring is a reactive approach, as it identifies issues after they impact the real users.)  

Eliminates privacy issues. Active monitoring does not use real data for analysis. Thus, there’s no concern over protecting user data privacy. 

Can be used for load testing. IT teams can build standardized load testing scenarios to test the system performance under varying loads. It helps identify potential performance issues that cannot be identified using packet capture.

Advantages of passive monitoring

Provides detailed insights. Since passive monitoring uses so much real-time data, you can get very in-depth information on usage patterns. Mature organizations even feed that data into machine learning models for classification and clustering tasks with higher accuracy.

Identifies complex problems. Passive monitoring helps identify issues that happen intermittently, which would otherwise go undetected through active monitoring. 

Costs less than active monitoring. Passive monitoring is easier to set up than active monitoring. No resources are required for synthetic traffic generation. Thus, it can be more cost-efficient, especially for large enterprises. 

Identify security issues before they could occur. Large-scale real-time traffic analysis helps detect potential security breaches. 

Disadvantages

Despite the above advantages, both methods have cons. You must consider them when leveraging these methods. 

Drawbacks of active monitoring

• Issues related to data generation. For example, extra synthetic traffic generated in active network monitoring can congest the actual network traffic. Additionally, active monitoring can impact the normal operations of the networks as it is intrusive in nature. 
• Accuracy issues. Since active monitoring generates artificial data, the accuracy of the results can be lower than in passive monitoring.
• Additional costs. Separate resources are required to set up, generate traffic, and set up synthetic transactions. Thus, companies will have to incur additional costs.

Drawbacks of passive monitoring

• Issues related to high data volume. Passive Monitoring needs more storage capacity and processing power to process the large volume of captured data. 
• Reactive issue identification. Passive monitoring needs continuous user action to perform the underlying tests. Thus, if there is less traffic, hidden issues may only be revealed once they impact users. 
• User data privacy issues. The real data captured by passive monitoring systems may include private and sensitive data, violating data privacy regulations. Therefore, organizations practicing this method must try to stop capturing such data. 

Smart organizations harness both monitoring options

As mentioned in this article, active and passive monitoring mainly differ from the data used for testing various performance metrics. Both approaches have different advantages over the others due to the nature of the data and the monitoring approach used. While there are several advantages, these approaches come with several cons, as described in the article. You may also need to consider them before incorporating these methods into your organization.