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Migrating from Kamon 1.x to 2.0 #

Most of the work put into Kamon 2.0 has been geared towards having cleaner, easier to use APIs and instrumentation mechanisms and some of those improvements resulted in breaking changes that we are enumerating below. The amount of effort needed to upgrade can vary based on whether you were just using plain Kamon to gather standard metrics or you were actively using the APIs to manage context and create your own metrics and traces, but in general this should not be a big effort and you are like to remove lines rather than add.

There is no step by step guide to migrate. Our suggestion would be to read every item and apply the changes if needed. If there is something preventing you from upgrade and not mentioned here, please drop a line on Gitter and we’ll give you a hand and update this guide accordingly.

There is a new Kamon.init() method #

The Kamon.init() method takes care of a few common tasks performed during initialization:

  • It will try to attach the instrumentation agent to the current JVM if you have the bundle dependency (more on that below).
  • It will scan your classpath for modules and automatically start them.
  • It can optionally take a new Config instance to be used by Kamon.

If you were manually calling Kamon.loadReportersFromConfig() and/or Kamon.addReporter(...), you don’t need to do so anymore.

A single call to Kamon.init() as the first line in your main method should be enough to set everything up!

We moved from AspectJ to Kanela #

As of this release, we are only shipping instrumentation created using our brand new instrumentation agent: Kanela, which is the result of many months of hard work towards simplifying how instrumentation is created and applied in runtime. Kanela used ByteBuddy and is Open Source as well, feel free to dig into the code and help us make it better!

The New Kamon Bundle #

There is a new package we are distributing called kamon-bundle. The bundle, as you might imagine, bundles all instrumentation modules available in Kamon and the Kanela agent and it becomes the preferred way of installing Kamon in any application. The bundle:

  • Only has a dependency on kamon-core.
  • Will automatically attach the agent when Kamon.init() is called.
  • Helps you stay up to date since the only dependency you will ever need to update is the bundle dependency.

We are still releasing and publishing all modules as independent libraries in case you want to continue adding them as in the previous Kamon versions.

The way to register kamon reporters has changed:

// Kamon 1.x

// Kamon 2.0
Kamon.registerModule("reporter name", reporter);

Metrics are now Tagged instead of Refined #

The refine method has been renamed to withTag, which return a new instrument with the specified tags. This also allows for chaining calls to withTag and the parent tags will be preserved.

Also, it was possible to call instrument actions directly on a metric (see the example below) which would result in recording values on an instrument without any tags. In order to keep the separation between a metric and its instruments as clearly defined as possible, those APIs are no longer available and if you were doing this, you will need to explicitly call withoutTags to get the instrument without tags:

val counter = Kamon.counter("my-counter")

// Kamon 1.x
counter.refine("zone", "east").increment()

// Kamon 2.0
counter.withTag("zone", "east").increment()

Metrics changes #

Gauges changed as show below:

// Kamon 1.x

// Kamon 2.0

Context Tags #

One super common pattern we see with most of our users is the need to propagate a few bits of information across all microservices and we set had the “broadcast strings” feature for that, but it wasn’t as simple to use as we would like it to be, specially because it was mandatory to add explicit configuration and mappings for it to work properly.

To replace that feature, we introduced Context Tags, which are simple key/value pairs built on top of the very same abstraction that we use for instrument and span tags, but attached to the Context. With this release, the Context can hold both entries and tags, and since tags are made out of known types (String, Long or Boolean) automatically propagate them without additional intervention across HTTP and Binary propagation channels.

Context instances are immutable and you can create a new Context that includes or overrides certain tag using the withTag function as show below:

val context = Context.Empty
  .withTag("zone", "east")
  .withTag("shard", 42)
  .withTag("has-gpu", true)

Remember though, creating a Context has nothing to do with making it current or propagating it, make sure you use the appropriate functions for that (see more below).

Tags and Metrics Names #

You might notice that some metrics names have changed. A prime example is kamon-system-metrics. The reason why that happened was that our naming approach was flawed. In Kamon 1.x was the first time we started using tags in all of our integrations and we just went sort of crazy with it, more than we should have. When moving to 2.x we tried to make sure that the definition of “what” is being measured is completely encoded in the metric name and the definition of “from where” is being measured is completely encoded in the tags.

There are a few things that helped us test whether the metric/tag were right, one of them was asking ourselves: if we aggregated all timeseries of the same metric, would the resulting timeseries be completely useless? In cases like host.cpu where the same metric had different tags for free and used CPU it was obviously a bad choice since even though the two measurements come from the same thing, their meanings are really different. Same goes with jvm.memory and pretty much anything where we had something and the opposite of that something encoded in tags of the same metric.

Rest assured that we really don’t want to make any more breaking changes like that. It was just a necessary pain to have a consistent behavior.

In-Process Context Propagation Changes #

All the functions used to temporarily store a Context in the current Thread changed their name prefix from with to runWith. For example, Kamon.withSpan became Kamon.runWithSpan and so on. The semantics are exactly the same, just the names changed.

Filter Changes #

Starting in this release, we will no longer host filters under the kamon.util.filters configuration path. Instead, each module requiring filter will define its own paths for them, which will make them easier to manage. The structure of filters remain exactly the same, though, so you can keep your includes/excludes, just need to move them to the right place.

The Akka instrumentation uses filters heavily and all its filters have been moved to a new location under the Akka path. The new filter paths are:

  • kamon.instrumentation.akka.filters.actors.track controls which actors will get dedicated metrics.
  • kamon.instrumentation.akka.filters.actors.trace controls which actors will participate in traces that have already been started in the application (i.e. just generate Spans for the messages they process).
  • kamon.instrumentation.akka.filters.actors.start-trace controls which actors will participate in traces and optionally start new traces if none is available when they start processing their messages.
  • kamon.instrumentation.akka.filters.routers controls which routers will get dedicated metrics.
  • kamon.instrumentation.akka.filters.dispatchers controls which dispatchers will get dedicated metrics.
  • kamon.instrumentation.akka.filters.groups controls the actor grouping mechanism.

You can read more about the filters and their effects on the Akka Instrumentation section of the documentation.

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