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Alright, so I'm going to get rolling here. How's everybody doing? I'm Matt Sanders.
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I work for Librato on a product called Metric, which some of you may have seen. Today, I'm excited to talk to you about ActiveSupport::Notifications.
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Is there a way I can turn this down just a little bit? How do I sound to you guys, am I too loud?
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Alright, awesome! We'll carry on. I'm excited to talk to you today about ActiveSupport::Notifications.
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As probably most of you know, ActiveSupport is one of the libraries that makes up Rails. One of the changes that came in Rails 3 was that a lot of its components became more modular.
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We can use it inside Rails and outside of Rails. ActiveSupport::Notifications is one of those things that came in Rails 3 and is a subsection of ActiveSupport.
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The reason I'm excited about it is that I think it offers you the capability to track what's going on in your applications, both during development and especially in production.
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A lot of the information you probably already want to know about your apps is being instrumented for you already. Rails uses this extensively internally.
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So, let's cut to the chase and look at the basics. There are basically two things you need to know about how ActiveSupport::Notifications works: subscribers and instrument calls.
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When you set up a subscriber, you're essentially saying, 'For any message with this name, when instrumentation with that name gets called, let me know.'
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You want to do something with that; send me the information associated with that event.
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So, subscribers are setting up that callback to receive the event and do something with it. Instrument calls are actually triggering that the event is firing.
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The method name, which is the message name, is how they communicate with each other.
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Now, why is this important? Why do we even care in the first place? As I said before, there's a lot of valuable data that Rails already provides.
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This gives you an opportunity to move away from the traditional one-to-one approach, which is often limited. You know, when I was interested in finding out what was wrong with a part of my application, I would throw debug statements in the logs.
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Now, you can say there's a bunch of things I want to do when this thing fires. There are many ways I want to track what's going on, and it's super easy to set that up.
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This is a quote from Peter Drucker, who is considered the father of modern management. I believe it's true: What we measure, what we look at every day, determines what we work on, what we get excited about, and what we take to the next level.
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As programmers, we tend to focus on the things that are attractive to us, which may not always be the most important aspects of our application.
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Often, we lack visibility into what's happening in our application and how people are using it. This excites me because it's an opportunity to hone in on what matters and gain insights that can enhance both your application and user experience.
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Another important point is that your production environment is not the same as your development environment.
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Even if you're running on the same operating system, different things are happening in the background when you're in production.
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You're likely running on multiple nodes or different versions of components, making it vital to capture that data in production to inform your decision-making.
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Let’s say you have a service that appears to be functioning well, with a response time under a hundred milliseconds.
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Suddenly, there's a significant spike, and the service slows down fourfold. What happened?
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When this occurs, ideally, you should be tracking all the things you care about to diagnose the problem effectively.
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This way, you can investigate calmly rather than scrambling through logs to understand the chaos.
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In our core applications, ActiveSupport::Notifications gives us the capacity to gain sharp insights into these issues.
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Earlier, I mentioned two core ideas: subscribers and instrumentation events.
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The message name drives communication between the two. Now, let’s explore how instrumentation works.
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There’s one required argument: the message name. For something like this, we may only care about whether the event occurred.
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Any subsequent arguments in the hash will be passed along as a payload.
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For example, if you're capturing the email address of a new sign-up, passing this along ensures that all subscribers receive that information.
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Here’s what the actual payload looks like: it includes the message name, start and end times, and a unique message ID.
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The message ID helps differentiate between messages for the dispatcher.
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Most use cases can ignore this unique ID and focus on the hash that represents your payload!
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In the block form of this method, any code you run inside will get automatic timing.
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This acts like a combination of a benchmark and a logging statement.
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The payload arguments are the same, but the different start and end times give you clarity on duration.
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If an exception occurs during this process, an additional argument will indicate the exception name and its message.
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One common misunderstanding is the expectation that you'll receive the exception object itself; instead, you'll only receive the name of the exception.
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In subscriber setup, you're going to want to use milliseconds for all timing.
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You can calculate the duration manually by multiplying the duration in seconds by a thousand, but ActiveSupport::Notifications also provides an event class.
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This class allows you to include your arguments without worrying about their order.
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From our talk last night, it's always preferable to call arguments by name rather than by order.
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You’ll receive an object containing all passed arguments, and the duration will be calculated for you.
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The event helper class provides a useful trick for linking events. You can determine whether one event happened completely within another by using this parent_of method.
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For example, if one event is triggered entirely inside another, the parent_of method returns true.
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Additionally, you can use regular expressions instead of strings to match message names; this minimizes the need for multiple subscriber definitions.
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Previously, I mentioned that Rails provides a wealth of instrumentation for you; let's get to the good stuff.
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This is not a complete list, but here are the primary events exposed by Rails by default.
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You’ll notice events related to ActionController for dispatching requests, caching stuff, ActionMailer for delivering and receiving mail.
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There are even events in ActionView for rendering, as well as for caching operations in ActiveSupport.
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ActiveRecord has one notable event that is crucial since it runs any time a query is executed.
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By tapping into this unique instrumentation and applying conditional monitoring, you can gather fascinating data.
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It’s important to mention that previous examples show the namespaced dot notation common in the monitoring realm.
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Some tools, like Graphite, translate these names into folders, allowing for visible separation, which is typically left to right.
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In Rails, it’s opposite, always right to left, so just keep that in mind.
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Let's dive into one of these events; specifically, we can analyze the ActionController's process action event.
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This event provides valuable information about the controller, action, format, status code, and timing data.
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With this information, we can conduct various analyses.
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The graph you've seen here illustrates the total request time versus time spent in the view and the database.
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In such cases, we can quickly ascertain that our database is not the bottleneck, as we're spending more time on view rendering.
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If we observe peculiar spikes in the request time not accounted for by the database, there might be an issue with external service dependencies.
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This presents an opportune moment to consider caching solutions.
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You can also monitor how many requests each of the servers in your cluster handle.
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Ideally, if the load balancer works efficiently, the load should be evenly distributed. If not, it raises critical questions.
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Here, we’re considering slow requests. By defining an arbitrary threshold (e.g., 200 milliseconds), we flag slow requests during monitoring.
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As the total number of requests rises, it becomes essential to analyze whether the slowness is due to high request volumes or inherent application slowdown.
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We can analyze the slowest request patterns across different servers, helping pinpoint where optimization efforts should occur.
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This highlights the importance of using the existing instrumentation information effectively.
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Furthermore, ActiveRecord fires an event each time it executes a query.
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You collect the duration, retrieve the entire query, and obtain parameter bindings if applicable.
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You receive a name argument for identifying the model associated with the query, aiding in performance assessments.
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You can leverage this information to create customized integrations.
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Consider models that are fetched frequently and reevaluate their necessity. Caching query results can significantly reduce database load.
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It’s about elevating visibility into your application to optimize its performance effectively.
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This opportunity to enhance our applications and metrics is exciting as it streamlines tracking critical success factors.
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I think performance monitoring and instrumentation shouldn't feel burdensome. Instead, it should offer clarity around core application metrics.
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Ultimately, what this boils down to is the actionable visibility you gain using ActiveSupport::Notifications.
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It creates opportunities to improve our application's performance through insightful practice.
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Now, let's pivot to how you can create your own events.
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Probably the simplest way to use this is to log your desired events using Rails logger.
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You can streamline your logs for machine readability or utilize products like Papertrail, which is fantastic for real-time searchable logs.
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Another fantastic tool is New Relic, where you can easily create custom events.
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Moreover, you can combine it with StatsD for effective collection of metrics.
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StatsD is a lightweight application that collects and forwards metrics without slowing down your app.
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You can utilize libraries to integrate well with existing setups, further enhancing your logging capabilities.
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This integration allows you to stash data for later usage while maintaining efficient processing.
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You can define patterns that allow your subscribers to operate over multiple notifications seamlessly.
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Remember, all subscribers can be triggered by a single event within your controller.
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Understanding performance is essential; whatever runs in your instrumentation block will complete before all related subscribers run sequentially.
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Avoid long-running operations in your subscribers, as they can introduce latency in request handling.
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Background operations can run asynchronously, but when performance is crucial, keep your instrumentation fast.
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ActiveSupport Notifications is straightforward and manageable; you can customize it extensively.
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While I don't recommend using unsubscribe method often due to its potential impact on performance.
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When a message invokes, the dispatcher learns if anyone cares about this event and keeps a cache regarding it.
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Careful when modifying subscribers, as it can invalidate that cache, slowing down your application's responsiveness.
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Hopefully, you've now covered the basics of ActiveSupport Notifications. Any outstanding questions?
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If there's anything confusing, please feel free to ask!
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Now, let’s talk about conditional instrumentation—a simple but powerful practice.
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Begin subscribers by verifying your relevance, returning immediately if the event does not concern you.
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This decision accelerates your subscriber operations significantly.
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I encourage the use of various tools that allow selective feature rollout, such as Rollout.
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This service enables beta testing of features among select users, gathering insightful feedback before widening your focus.
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You can enable or disable instrumentation dynamically based on customer-specific needs.
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Wrap checks around the Rollout functionality to avoid bugs appearing due to Redis or other service unavailability.
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Incorporate notification bot integrations, like Campfire, to streamline operations and collect user feedback or alerts efficiently.
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When a service outage occurs, you can respond promptly to resolve technical hiccups.
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Ruby code can reduce repeated calls to ActiveSupport::Notifications for clarity and simplicity.
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By leveraging your Application Controller, you could streamline instrumentation calls.
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Additionally, observe the possibility of shared patterns across Models using modular setups.
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You may also notice prevalent repetitiveness when defining subscribers.
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Fortunately, ActiveSupport has a separate LogSubscriber library that alleviates it.
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This setup allows for dynamic logging without excessive manual annotation.
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Ensure you set this up correctly; it requires associations with parent namespaces.
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From here, access log methods directly within LogSubscribers for ease.
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Most crucial services leverage LogSubscribers for simplifying operational logging.
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We can also use this methodology beyond Rails, allowing for effective instrumentation in non-Rails code.
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Even utilizing gems outside Rails can amplify your code's visibility without compromising its core functionality.
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Open source projects have adopted this instrumentation approach, elevating their communities.
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For example, Faraday middleware emits instrumentation across entire request environments.
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On top of that, various gems already utilize this pattern, such as Excon.
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Integrating instrumentation means you can create unique event signatures for enhanced clarity.
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This considerably lowers the barrier for identifying performance issues without extensive overhead.
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Lograge, for instance, converts verbose logs into concise and readable records.
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The transformation provides parsable logs from multi-threaded environments seamlessly.
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Engage with interesting projects leveraging ActiveSupport Notifications for better insights.
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Review log subscribers in Rails for further inspiration and flexibility in your work.
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Remember, tools only become powerful through collective utilization and understanding within a community.
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It’s critical for teams to communicate and establish clear guidelines for implementing and using instrumentation.
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To streamline all subscribers and initializers, clump them together to maximize visibility.
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Combining client-serving operations with instrumentation can create confusion and inefficient usage.
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Consider using insights gained for operational tasks while maintaining distinct functionalities for user-focused jobs.
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Thanks for your time today! I hope you feel inspired to continue exploring the incredible potential of ActiveSupport Notifications.
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Engage with your applications deeply; identify what matters to you, your team, and your users.
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Assess your conditions for success meticulously. Explore the opportunities here.
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How can you better utilize insights from ActiveSupport Notifications? Thank you!
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Thank you!
