What Is Distributed Tracing? Key Concepts and Definition

Back in the day, monitoring applications from end to end was—for the most part—significantly easier than it is today. Though the basics of instrumentation and observability for metrics like CPU, memory, and I/O throughput haven’t changed, the way applications are built has changed significantly. There were, at most, a handful of application servers and likely a single database server. This legacy infrastructure topology was monolithic by nature, and the ability to monitor the entire stack was entirely vertical, with minimal horizontal tentacles spanning within the organization’s ecosystem. Whenever I think about a monolithic application, I reflect on the days of managing an enterprise resource planning (ERP) system like Microsoft Dynamics or SAP. Both are examples of modular applications with facets like accounts payable, accounts receivable, inventory management, timekeeping, and so forth. Though they were individual modules, these applications ran in a monolithic mainframe computer in some cases. More modern ERP systems are examples of a distributed system. This monolithic application architecture allowed IT departments to identify and track issues occurring within it more easily. In the past, agent-based monitoring systems would continuously monitor the underlying infrastructure for anything requiring an alert. While virtualization began to change the way infrastructure monitoring took place, recent developments in infrastructure have completely changed the entire paradigm. This includes the introduction of infrastructure advancements—such as containers and microservices—which often run in a “serverless” fashion. Then, in the case of containers, they’re ephemeral and need an entirely new way to monitor your applications. These major changes in the way applications are deployed manifested as a more distributed topology in nature, forcing organizations to determine new methods to track requests as they flow through the application stack. Thus, distributed tracing was born from absolute necessity.

The Transformation of Distributed Tracing

Trends in application development—like DevOps—have caused organizations to investigate ways for their application deployments to become more portable and agile. At the same time, the dawn of the public cloud provided offerings like serverless functions and container services, which allow for new architectures. This newfound agility means applications built on top of a series of microservices can be deployed faster and in a less-coupled manner in comparison to previous methodologies where applications were tightly bound to the underlying infrastructure. This increase in deployment velocity doesn’t impede the ability of microservices to be fully vetted and tested, however. Given the smaller footprint of the application, it’s also far easier to maintain than a more monolithic application stack.

Figure 1 This diagram shows the microservices architecture

With the advent of microservices architectures as depicted in Figure 1, it isn’t surprising this new, quick, and efficient method would be developed for deployment. Beyond mere infrastructure changes, frameworks like Simple Object Access Protocol (SOAP) have been replaced with a series of REST API calls between application components. Though these services could be deployed to the same infrastructure, this didn’t provide the level of agility many development teams were seeking. This process also didn’t take advantage of cloud-native functionality. Modern applications are no longer tightly bound to the underlying hardware, nor are they collocated with other services. The solution to this issue came through using containers and container orchestration frameworks like Kubernetes. A container is a piece of software built to bundle an application and all its dependencies so it can run efficiently and independently from other components within the application stack. A container runs an individual service and may only exist for the life of a process. The isolation of the software within the container away from the infrastructure and operating system can also ensure the stability of the applications, regardless of the underlying infrastructure. The container can float between environments with ease. This continued nimbleness of containers ensures microservices exist in such a way they can quickly be created and destroyed with minimal interruption to the business. Containers facilitate the distributed outward growth many organizations experience today when deploying IT resources. As an additional comparison, virtual machines provide an abstract layer for the hardware containers by providing an abstract layer one step higher—the operating system.

Wait, Isn’t Distributed Tracing Just Logging?

Sort of, but not really. Distributed tracing still logs information and traces data but in a different context. Any infrastructure component of a distributed topology can generate logs, but logging is for humans to consume and evaluate. This requires someone to consume and digest the contents of a log—or even multiple logs—to pinpoint where issues have occurred. If you’ve ever had to troubleshoot cluster logs for a Windows Server Failover Cluster or an open-source solution like Pacemaker, you’ll know this can be a long, arduous, and unfruitful process. Logging is usually a reactive mechanism, generating information based on a given event. For example, SQL Server logs certain events within its own error logs, such as successful database backup events. Though there are methods to disable this level of logging, SQL Server logs it by default out of the box. In this case, for the message to be logged, a database backup event must occur first. If the event doesn’t occur, the log message isn’t generated. Distributed tracing logs information, but it does it far differently.

If It Isn’t Logging, What Is Distributed Tracing?

Distributed tracing is a method used to track requests or transmissions (which can be agnostic in nature) throughout a distributed topology of infrastructure components. At a high level, requests are usually tagged with a unique identifier, which facilitates end-to-end tracing of the transmission. This continued monitoring of the request allows an organization to have top-down visibility at essentially every level of the infrastructure stack and observability into latency throughout the entire application stack. This is different from logging because the transmission itself is tagged and cataloged as it travels throughout the entire ecosystem. This continued cataloging of metadata across containers and microservices and the transmission between them provides IT teams with far deeper insight into—and context for—the transmissions. This deeper visibility into the transmissions subsequently allows for greater accuracy and insight into where errors have occurred and allows engineers to debug bottlenecks, whether they’re in the Java application code or the database back end.

Does Distributed Tracing Replace Logging Tools?

Keep in mind logging and distributed tracing can operate together in harmony. Logging is still the foundation of many IT departments, and performing one doesn’t mean you can’t perform the other. As organizations continue their journey into the realm of containers and microservices, distributed tracing offers up a complementary method to ensure infrastructure resiliency. Incidentally, as an IT professional of more than 20 years, I’d say having an abundance of information is significantly better than a lack of it. Having all the data available to assist in your troubleshooting efforts can get you to the root cause of performance issues, even for events you didn’t observe in real time. So don’t be afraid to use both logging and distributed tracing solutions when and where appropriate.

How Does Distributed Tracing Work?

As previously mentioned, transmissions (or requests) are tagged. The tagging process begins in the application development, where libraries from the monitoring are added to the application. Let’s use a common example of an HTTP request. Once the application is appropriately tagged, requests continue to move through the various microservices. As they travel through the ecosystem, every operation performed on the requests is called a span. The initial request is considered the “parent span,” and every subsequent operation is a “child span.” Each child span also appends a unique trace ID in conjunction with the parent span identifier. Each span is a distinct marker of the request’s voyage. Each marker contains information about the microservice performing the work at that point in time. This information can include the following details:

• Service name
• Contextual information about the event
• Tagging information, such as database host, session IDs, and HTTP methods
• Information in the event of failures
• Trace ID for each execution

Distributed tracing tools can correlate all the data from the various spans of the request and transform them into useful visualizations. Often, these visualizations are shown through some manner of web interface with a dashboard view. The ability to provide this information in an efficient way allows IT personnel to quickly identify and respond to application performance issues. These tools can also help gather performance monitoring metrics to indicate how well each microservice performs. IT teams can then make appropriate adjustments to better fine-tune the environment and meet resource demands.

Why Is Distributed Tracing So Important?

As organizations evolve into the realm of microservices, traditional logging may not be sufficient to keep up with demand. Imagine having an extremely busy application and attempting to apply traditional logging techniques against it. It would be bogged down by the sheer nature of the logging itself. With distributed tracing, the logging is moved to each individual span of the request, allowing for a lightweight and versatile way to provide in-depth metrics, including the overall health of the ecosystem. Distributed tracing is a must-have for any organization looking to implement microservices or containers into their environments. Without it, you’ll spend countless hours sifting through log after log, never finding the Holy Grail. Learn how SolarWinds^® Hybrid Cloud Observability can help organizations of any size modernize their IT agility through an integrated IT infrastructure, application, and database performance monitoring solution.