AEM OSGi Service and Component Monitoring

AEM is a juggernaut in the content and experience management space. It is used far and wide from nonprofits to the most profitable companies our modern world has seen. AEM is also an incredible monolith in the budding world of microservices and soon the up-coming world of functions as a service.

Engineers and users of the AEM as a platform write code which resides within bundles. These bundles create little pockets, islands, where the code runs and is able to specifically import and expose code, libraries, interfaces, APIs. It also allows for service and OSGi component definitions that can dictate their operational conditions and interlocking service dependencies/references.

It is quite typical for customer needs to justify creating extensive APIs and services to use for web content, mobile content, and API services to anything in-between, like retail displays and internet of things.

AEM also lives somewhat in its own a world – a world where open tech and products often require additional work for import. If an API or persistence engine driver doesn’t provide OSGi manifests, then the system (Apache Felix) doesn’t know how to load it. This is often the case. Couple this with the fact that AEM, formerly CQ, has been around for a little over a decade, and it’s own feature richness and you end up painting a picture. A picture of a self-contained ecosystem that occasionally yearns for the coasts of its neighbors (i.e. other tech).

Configuration management, property encryption are an example of this. AEM leverages the OSGi property configs coupled with run modes to layer together something that resembles Hashicorps Consul, etcd, or other key-value stores. Live config changes in say, production, can yield random and in-consistent outcomes from the merged configs like those stored in the JCR. Cases like this introduce service and component availability issues within an otherwise healthy AEM appserver monolith.


And so most devops, cloud engineering, etc… teams monitor an instances uptime by pinging prescribed endpoints, monitoring for disk usage, free space, CPU load, etc… Monitoring memory utilization requires something that can introspect the JVM as the 8-16-32 gigs of RAM you allocate to the JVM running AEM are taken pretty right away at startup.

I had been on a number of high profile projects where we ran into random service outages and performance inconsistencies. These were typically caused by continuous code delivery mechanisms causes bundles to rise and fall along with their components and services. Frequent installations in and of itself are not nefarious, but occasionally set a chain of events in motion that can render inconsistent service states. That is why in April of last year I created a crude monitoring framework for monitoring OSGi services and components; the osgi-service-monitor.

OSGI Service Monitor

At its heart, the monitor set to loosely bind to other service references, and provide an ecosystem consistent polling “function” that allowed for other service implementations to watch for success and failure states. The monitors were termed ServiceMonitors and the watchers were termed NotificationDeliveryAgents. The ServiceMonitors crucially obtained, checked for, and guarded against missing, faulty, or failed service references and would report state to the NotificationDeliveryAgents. This system worked well for a variety of CITYTECHs clients at the time.

Despite decent adoption internally, the system was in need of configuration options, defined polling intervals, dashboards, outcome persistence, etc… This would be critical in releasing such a framework to a broader audience, though that was never done.


Early in 2014 I set out to create the second version, a complete re-write of what was formerly the osgi-service-monitor. I called this new project AEM Canary. Out of the box, Canary set to build on the old monitor framework covering the following functionality:

  • Monitor functionality with service annotation support defining when and how a monitor fires
  • Notification agent support to handle and react to failures for a particular monitor or monitors once a defined threshold had been met or exceeded
  • Response handlers meant to react to poll responses, regardless of the state
  • Persistence to the JCR
  • Additional JMX data
  • Useful monitors OOTB (blocked agent queue, sling event monitoring, exception listeners, etc…)
  • A graphical dashboard for viewing and interacting with the monitors and response data

Under the hood, Canary was far more complex than the 1st iteration of the framework. The core of the framework used an Actor pattern to handle message passing between the monitors, wrapped in actors. A sort of “mission control”-type service bridge the gap between services coming up and down in the OSGi ecosystem with the generated actors. Quartz was utilized in providing the critical timed execution, polling.

The actor framework, provided by GPars, allowed each unit to fire and communicate with one another via the actor’s inbox without worrying about concurrency or timing usage. Several years later, after development, I think it’s fair to admit that an Actor framework was overkill and perhaps unnecessary.

In the end, by the time I was close to finishing AEM Canary, AEM 6.0 was launched with a health check project that had made its way into the product. The project was pulled into the Sling[] ecosystem as Sling Health Check. I ended up more or less dropping the project, moving on to work on some non-AEM-based platforms, like building mobile backends in PlayFramework. Oh. Actors again, you say? Yes.

Anyway, it was a fun side project. A project I wrote about a few times and tried to promote, but at the end of the day was a good learning lesson in engineer maturity, framework maturity, and toolchain adoption by a community.

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