We've also declared that this service listens on port 80, and that we want there to be 10 instances, or replicas, of the service running. Once you send an introductory message to someone, we won't show them to you again on OkCupid until they like you back. When you want to do maintenance on a machine, you're going to need to stop all the instances running there, but those instances might be necessary for performance. What’s the etiquette when dating casually? After serving traffic with high availably for several years, you get more requirements: One of the inconvenient implementation details of Membership is that the number of instances of each service has to be pre-configured, and changing the configuration is tricky, so it's challenging to scale. deploy new versions of software services. If we want to scale services up or down, just change that number replicas: 10 to replicas: 50 or anything else, and Kubernetes will start up the instances for you. New comments cannot be posted and votes cannot be cast, Press J to jump to the feed. Of course, our actual backend is much more complex than this, on the order of 100 different services rather than just the 5 pictured above. Did they remove search? Under the new messaging regime, messages aren't exchanged in the "normal" sense until you've both liked each other. There might be unused compute resources on other machines, so you could move all the service instances off of the machine onto other available machines. Technically you can still. Remember that the number of instances is pre-configured in Membership, so you can't have the new ones and the old ones running at the same time. This spring, I took the week to finally dive further into Espresso testing. Search was neat sometimes to use keywords to see who might be in to things you are. If you have those two pieces, then you've got the tools you need to solve high availability. Kubernetes maintains a DNS entry accessible as the name doubletake-service that resolves to one of the working service instances. Senior Software Engineer - Backend at OkCupid. I've automated apps with this tool before, but there's one issue with Espresso testing that I've always struggled with: network mocking. Seriously - I wrote to someone they were in my "liked" list, once it was sent, they were completely removed from my list. Profiles . Nothing yet, except a bunch of emails about new messages that I am still unable to find :/. We need to be able to do maintenance on our software with no disruption of service, for example deploying a new version. I could write a whole article about updating glibc versions and why containers are so much nicer to deal with, but let's get back to talking about Kubernetes. In this example doubletake-service:v123 would identify a Docker image version 123. Daemontools was not designed for rebalancing instances across different machines. Upon reinstall, and starting a new account, I noticed I only have doubletake, likes, messages, and profile on the app. What gives? Googling and searching here isn’t showing me anything. Let's state our goals so we can choose a solution: The simple and effective approach is to run multiple instances of each of our services spread across multiple machines. No more wasted time or frustration. Being able to search for matches based on what I'm looking for is the main reason why I've been coming back to OkCupid. The services are long-running server processes deployed on 100 or so machines, and we need up to 100 instances of some services. As we add machines and scale up services, we can run into an uneven balance of instances running on different machines. You'd better not pick an instance that's down for any reason, or the service will appear unavailable. They do not include any mention of daemontools, because that's an implementation detail, not an objective. Let's use an example of one machine losing power suddenly. On OkCupid, those connections start with a message. Not even the person, but literally I can't even see what I just sent? This happens once every few weeks, and when it's time to update, you get to choose when to restart the app. It's a registry of instances of each service that is running that includes information about where the instance is running. Who ever thought this was a good idea is like the principals that ban ibuprofen in school. Wherever that ends up being, other software needs to know how to contact them. So I'm assuming they hide them so you don't rewrite? When we want to deploy a new version of the backend, we only need to do maintenance on the services that are actually changing, for example just notification-service. We need to do be able to do maintenance on the machines themselves such as upgrading the operating system, which means an hour or so of nothing running on the machine.

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