Containers and Real-Time Resource Monitoring

on May 30, 2017

Are you monitoring your containers’ resources in real time? If not, then you’re probably not monitoring as effectively as possible. In a fast-moving, dynamic microservices environment, monitoring data that is even seconds old may no longer be actionable. To prevent disruptions, you need real-time monitoring.

In this post, I explain why real-time monitoring of container resources is important, and which types of container metrics you should focus on monitoring in real time.

And just to be clear up front, this isn’t a post endorsing any particular monitoring vendor’s toolset. While there are now plenty of container-ready monitoring platforms out there that can support real-time monitoring, I think it’s better to understand the underlying essentials of container monitoring, rather than focusing on the feature set of a particular product. If you know what to monitor in real time in order to keep your containerized infrastructure running healthily, you’ll be well-positioned to choose the best toolset to meet your real-time monitoring needs.


The Challenges of Real-Time Container Monitoring

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Before discussing how to perform real-time monitoring for containers, it’s worth pointing out the special challenges that arise from monitoring containers in real time.

The most obvious is that, in a containerized environment, components disappear all the time by design. In a legacy environment, you focused on monitoring servers and apps that were relatively static. But containers spin up and down constantly.

As a result, there is a lot more monitoring in a containerized environment. By extension, there is a lot more noise. Separating meaningful data from noise is therefore more difficult, especially when you need instant monitoring insights and can’t waste time identifying noise.

Real-time monitoring can also be harder in a containerized environment because of the way Docker abstract containers away from the host. When you’re dealing with containers, you can’t simply run monitoring commands like top or ps from the host and get an accurate picture of what’s happening inside the containers.

Since logging into containers to peer inside in real time for monitoring purposes is not feasible at scale, the answer to this challenge is to use agents or another clever type of monitoring solution that provides real-time visibility into containers and the services they support.


What Can You Monitor?

Let’s now take a look at which real-time container metrics you can monitor. Taking Docker as the most obvious example (although much of the following applies to other container systems, including the Linux-native LXD), we can break real-time container metrics into four basic categories:


Docker can monitor the total memory used by an individual container, along with the amount of cache and swap memory, and the resident set size, or RSS, which represents memory used by processes and not cached or stored on disk, such as anonymous memory maps and stacks.

Both RSS and cache memory can be broken down into active and inactive memory. Minor (duplication or allocation) and major (full read from disk) page faults are also included in Docker’s memory statistics.


Docker monitors both user CPU time (CPU use by the processes themselves), and system CPU time (system calls by processes). If CPU throttling (limiting the time available for a given container) is being enforced, the throttling count and time for the container will also be reported.


For I/O, Docker monitors both the number of I/O operations and the volume of I/O in bytes. In both cases, it counts synchronous / asynchronous and read / write separately. Docker also provides a count of sectors (512-byte) read and written (reads/writes are counted together), and a count of operations currently in the queue.

Network Resources

Docker also reports overall network metrics for individual containers, including packet count, traffic volume in bytes, dropped packets, and transmit and receive errors.

And more…

Other metrics to consider are those involving storage (and storage-related performance metrics), as well as the total number of containers in use. In addition to container-specific metrics, it is, of course, important to monitor such traditional factors as overall system performance, traffic, patterns of user behavior, and application performance, all of which may directly or indirectly impact container activity.


The Best Ways to Monitor

Methods of monitoring and monitoring services are of course important as well. Docker’s native monitoring tools have a bare-bones interface, but many of the services which are built on or incorporate those tools have considerably greater capabilities, which may include non-Docker resource monitoring, dashboards, analytics at both the container and aggregate levels, and an API for alerts and other automated responses.

Many of these tools are easily integrated with Rancher, and can be used to monitor (and analyze) Rancher-specific resources, as well as those common to containers in general.


Why Is Container Monitoring Important?

Why is it important to monitor metrics such as these? Not surprisingly, the main reasons for monitoring containers closely parallel the main reasons for monitoring other applications: performance, error detection, and detection of anomalous behavior. In the case of containers, monitoring may help you detect problems at the system, container, and application levels.

This doesn’t mean, by the way, that the approach you take to container monitoring is identical to the one you use in traditional environments. As noted above, container monitoring presents particular challenges. But the benefits of container monitoring are the same in either case.


Real-Time Container Monitoring and Performance Optimization

Perhaps the most obvious metrics for monitoring container performance are those involving CPU and memory use. Is a specific container (or more typically, many or most instances of a container which compose a specific microservice) taking up too much CPU time, or too much memory? If so, then you have an opportunity to optimize performance by finding and fixing the problem.

The following are some specific strategies you can adopt to address performance issues that you can identify through real-time monitoring.

Throttling CPU

You may be able to solve some problems with excessive CPU use simply by enforcing CPU throttling. In other cases, however, such performance issues may be an indication of problems in design (at either the overall application or microservices level), or coding errors. Such performance-related problems may also show up in I/O or even network metrics.

Throttling can serve a function similar to that of traditional load-balancing, but it is important when confronted with CPU-related performance problems not to simply throttle and assume that will solve the problem. If a crucial service is using excessive CPU time, throttling it may simply degrade performance in other ways.

When faced with chronic CPU or memory problems or similar performance issues, it is important to look for bottlenecks at the design level, and application errors which may result in inefficient or incorrect use of memory, CPU services, or other resources.

Provisioning Resources

Performance problems may also result from inadequate provisioning of resources at the system level. You may need to provision more memory, more storage, more CPU access, or switch to a cloud service contract which gives you higher priority in accessing resources.

But Provisioning isn’t a Cure-All

As is the case with throttling, however, it is important not to simply provision more resources and hope that it will solve performance problems. You should first look at application architecture, microservice design, and possible functional problems at the coding level. You can’t fix design problems or bugs by throwing resources at them. You may be able to overcome the obvious and immediate inefficiencies that way, but other effects of the basic problem may continue undetected, resulting in even greater trouble at some point.


Container Monitoring: Bugs and Anomalous Behavior

Performance problems aren’t the only thing that real-time monitoring can help you find and address. The following are other types of issues (ones related to cost-optimization, security and user experience) that you should also keep in mind when performing real-time container monitoring.

Under-utilized Resources

A container that uses resources at a lower-than-expected level may be as serious an indication of trouble as overuse of resources. A credit-card authorization microservice which makes almost no use of I/O or network resources, for example, could be a sign of major problems—either with the authorization microservice itself, with one or more of the microservices which are supposed to use it, or with some other part of the application which may be only indirectly involved with credit authorization.

Suspicious Traffic

Container monitoring may uncover other forms of anomalous behavior as well. If containers are accessing (or simply requesting) resources which they would not ordinarily use, or if they show an unusual pattern of I/O or network traffic, it may indicate security problems.

Unmet needs

Anomalous container behavior may also be an indication of less alarming (but still important) problems, such as unexpected patterns of user activity. If users are (for legitimate reasons) accessing specific services at a much greater level than originally anticipated, for example, you may need to look at overall architecture, at patterns of deployment, or at the possibility of adding new services to meet currently unmet (or under-met) user needs.

So, while individual, here-one-millisecond-gone-the-next containers may not be persistent, everything else about your container ecosystem (infrastructure, stored data, user interactions, resource availability) does have an ongoing life, one which is strongly impacted by container behavior, and which may in turn have a major impact on your application’s performance, and on your organization’s bottom line. Real-time container monitoring isn’t just important. It’s a necessity.


Michael Churchman started as a scriptwriter, editor, and producer during the anything-goes early years of the game industry. He spent much of the ‘90s in the high-pressure bundled software industry, where the move from waterfall to faster release was well under way, and near-continuous release cycles and automated deployment were already de facto standards. During that time he developed a semi-automated system for managing localization in over fifteen languages. For the past ten years, he has been involved in the analysis of software development processes and related engineering management issues.


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