Keeping A Busy Portal Stable By Deploying Several Hundred Times Per Day

By | February 10, 2015

An interesting architecture with alternatives to big software providers.

Vinted is a peer-to-peer marketplace to sell, buy and swap clothes. It allows members to communicate directly and has the features of a social networking service.

Started in 2008 as a small community for Lithuanian girls, it developed into a worldwide project that serves over 7 million users in 8 different countries, and is growing non-stop, handling over 200 M requests per day.

Stats

  • 7 million users and growing
  • 2.5 million monthly active users
  • 200 million requests / day (pageviews + API calls)
  • 930 million photos
  • 80 TB raw space for image storage
  • 60 TB HDFS raw space for analytics data
  • 70% of traffic comes from mobile apps (API requests)
  • 3+ hours / week time spent per member
  • 25 million listed items
  • Over 220 servers:
    • 47 for internal tools (vpn, chef, monitoring, development, graphing, build, backups, etc.)
    • 38 for the Hadoop ecosystem
    • 34 for image processing and storage
    • 30 for Unicorn and microservices
    • 28 for MySQL databases, including replicas
    • 19 for the Sphinx search
    • 10 for resque background jobs
    • 10 for load balancing with Nginx
    • 6 for Kafka
    • 4 for Redis
    • 4 for email delivery

Technology Stack

Third Party Services

Core App And Services

Data Warehouse Stack

Servers And Provisioning

  • Mostly bare metal
  • Multiple data centers
  • CentOS
  • Chef for provisioning nearly everything
  • Berkshelf for managing Chef dependencies
  • Test Kitchen for running infrastructure tests on VMs
  • Ansible for rolling upgrades

Monitoring

  • Nagios for usual ops monitoring
  • Cacti for graphs and capacity planning
  • Graylog2 for app logs
  • Logstash for server logs
  • Kibana for querying logstash
  • Statsd for collecting real-time metrics from the app
  • Graphite for storing real-time metrics from the app
  • Grafana for creating beautiful dashboards with app metrics
  • Hubot for chat-based monitoring

Architecture Overview

  • Bare metal servers are used as a cheaper and more powerful alternative to cloud providers.
  • Servers hosted in 3 different data centers across Europe and the US.
  • Nginx frontends route HTTP requests to unicorn workers and do SSL termination.
  • Pacemaker is used to ensure high availability of Nginx servers.
  • In different countries, every Vinted portal has its own separate deployment and set of resources.
  • To increase machine utilization, most services that belong to multiple portals may run alongside each other on a single bare metal server. Chef recipes take care of unique port allocation and other separation concerns.
  • MySQL sharding is avoided by having a separate database for each portal.
  • In our largest portal, functional sharding is already happening, and a point where the single largest table will not fit into the server is months away.
  • Caching in Rails app uses custom mechanism with L2 cache that prevents spikes when the main cache is expired. Several caching strategies are used:
    • remote (in memcached)
    • local (in unicorn worker memory)
    • semi-local (in unicorn worker memory, falling back to memcached when local cache expires).
  • Several microservices are built around the core rails app, all with a clear purpose, like sending iOS push notifications, storing and serving brand names, storing and serving hashtags.
  • Microservices can be either per-portal, per-datacenter or global.
  • Multiple instances of each microservice are running for high availability.
  • HTTP-based microservices are balanced by Nginx.
  • Custom feeds for each member are implemented using Redis.
  • Catalog pages are loaded from the Sphinx index rather than MySQL when filters are used (custom size, color, etc.).
  • Images are processed by a separate Rails app.
  • Processed images are stored in GlusterFS.
  • Images are cached after 3rd hit, since the first few hits usually come from the uploader and an image may be rotated.
  • Memcached instances are sharded using twemproxy.

Team

  • over 150 full-time employees
  • 30 developers (backend, frontend, mobile)
  • 5 site reliability engineers
  • Main HQ in Vilnius, Lithuania
  • Offices in the USA, Germany, France, the Czech Republic and Poland

How The Company Works

  • Nearly all information is open to all employees
  • Using GitHub for almost everything (including to discuss company issues)
  • Real-time discussions in Slack
  • Everyone is free to participate in things that interest them
  • Autonomous teams
  • No seniority levels
  • Cross-functional development teams
  • No enforced process, teams decides how to manage themselves
  • Teams work on high-level problems and decide how to tackle them
  • Each team decides how, when and where they work
  • Teams hire for themselves when a need arises

Development Cycle

  • Developers branch from master.
  • Changes become pull requests in GitHub.
  • Jenkins runs Pronto to do static code and style checks, runs all tests on pull request branches and updates the GitHub pull request with a status.
  • Other developers review the change, add comments.
  • Pull requests may be updated multiple times with various fixes.
  • Jenkins runs all tests after each update.
  • Git history is cleaned up before merging with master to keep master history concise.
  • Accepted pull requests are merged into master.
  • Jenkins runs master build with all tests and triggers deployment jobs to roll out the new version.
  • Several minutes later, after the code has reached master branch, it is applied in production.
  • Pull requests are usually small.
  • Deployments happen ~300 times per day.

Avoiding Failures

Deploying hundreds of times per day does not mean everything always has to be broken, but keeping the site stable requires some discipline.

  • Deployments do not happen if tests are broken. There is no way to override this, master has to be green in order to deploy.
  • Automatic deployments are locked every night and during weekends.
  • Anyone can lock deployments manually from a Slack chat.
  • When deployments are locked, it is possible to “force” a deployment manually, from the Slack chat.
  • The team is very picky when it comes to reviewing code. The quality bar is set high. Tests are mandatory.
  • Before Unicorn reloads code, a warmup is done in production. It includes several requests to various critical parts of the portal.
  • During warmup, if any one request does not return 200 OK, the old code remains and deployment fails.
  • Occasionally a problem is not caught by tests / warmup, and broken code is released to production.
  • Errors are streamed to graylog server.
  • Alarms are trigerred if the error rate exceeds a threshold.
  • Error rate alarms and failed build notifications are reported instantly to a Slack chat.
  • All errors contain extra metadata: Unicorn worker host and pid, HTTP request details, git revision of the code that caused the problem, error backtrace.
  • Some types of “Fatal” errors are also reported directly to a Slack chat.
  • Each deployment log contains GitHub diff URL with all the changes.
  • If something breaks in production, it is easy to pinpoint the problem quickly due to a small changeset and instant error feedback.
  • Deployment details are reported to NewRelic, which makes it easy to troubleshoot introduction of performance bottlenecks.

Reducing Time To Production

There is a big focus on both fast and stable releases, the team is always working to keep build and deployment times as short as possible.

  • Full test suite contains >7000 tests and runs in ~3 minutes.
  • New tests are added constantly.
  • Jenkins runs on a bare metal machine with 32 CPU, 128G RAM and SSD drives.
  • Jenkins splits all tests into multiple chunks and runs them in parallel, aggregating final results.
  • Tests would run over 1 hour on an average machine without parallelisation.
  • Rails assets are pre-built in Jenkins for every commit in master branch.
  • During deployment, prebuilt assets are downloaded from jenkins and uploaded to all target servers.
  • BitTorrent is used when uploading a release to target servers.

Running Live Database Migrations

We can change the structure of our production MySQL databases without downtime, in most cases even at rush hour.

  • Database migrations can happen during any deployment
  • Percona toolkit’s pt-online-schema-change is used to run alters on a copy of the table, while keeping it in sync with the original, and to switch the copy with the original when the change is done

Operations

Server Provisioning

  • Chef is used to provision nearly every aspect of our infrastructure.
  • SRE team does pull requests for infrastructure changes just like Development teams do for code changes.
  • Jenkins is verifying all Chef pull requests, running cross dependency checks, foodcritic, etc.
  • Chef code changes are reviewed in GitHub by the team.
  • Developers can make infrastructure change pull requests to Chef repository.
  • When pull requests are merged, Jenkins uploads changed Chef cookbooks and applies them in production.
  • Plans to spawn DigitalOcean droplets to run Chef kitchen tests with Jenkins.
  • Jenkins itself is configured with Chef, not using the web UI.

Monitoring

  • Cacti graphs server side metrics
  • Nagios checks for everything that can be up or down
  • Nagios health checks for some of our apps and services
  • Statsd / Graphite for tracking app metrics, like member logins, signups, database object creation
  • Grafana used for nice dashboards
  • Grafana dashboards can be described and created dynamically using Chef

Chat Ops

  • Hubot sits in Slack.
  • Slack rooms are subscribed to various event notifications via hubot-pubsub.
  • #deploy room shows information about deployments, with links to GitHub diffs, Jenkins console outputs, etc. Right here deployments can be triggered, locked and unlocked with simple chat commands.
  • #deploy-fail room shows only deployment failures.
  • #failboat room shows announcements about error rates and individual errors in production.
  • There multiple #failboat-* rooms that give information about cron failures, stuck resque jobs, nagios warnings, newrelic alerts.
  • Twice a day Graylog errors are crunched and cross-checked with GitHub, reports are generated and presented to the development team.
  • If someone mentions you in GitHub, Hubot gives you a link to the issue in a private message on Slack.
  • When an issue or pull request is created in GitHub, teams that are mentioned receive pings in their appropriate Slack rooms.
  • Graphite graphs can be queried and displayed in Slack chat via Hubot.
  • You can ask Hubot questions about infrastructure, i.e. as about the machines where a certain service is deployed. Hubot queries the Chef server to get the data.
  • Developers use Hubot notifications for certain events that happen in our app. For example, customer the support chatroom is automatically notified about possible fraud cases.
  • Hubot is integrated with the office netatmo module and can tell everyone what CO2, noise, temperature and humidity levels are.

Data warehouse stack

  • We ingest data from two sources:
    • Website event tracking data: impressions, clicks etc.
    • Database (MySQL) changes.
  • Most event tracking data is published to an HTTP endpoint from JavaScript/Android/iOS front-end apps. Some events are published to a local UDP socket by our core Ruby on Rails application. We chose UDP in order to avoid blocking the request.
  • There’s a service that listens on the UDP socket for new events, buffers them and periodically emits to a raw events’ topic in Kafka.
  • A stream processing service consumes the raw events topic, validates the events, encodes them in Avro format and emits to event-specific topics.
  • We keep our Avro schemas of events in a separate centralized schema registry service.
  • Invalid events are placed into a separate Kafka topic for possible correction.
  • We use LinkedIn’s Camus job to offload events from event-specific topics to HDFS incrementally. Time to Hadoop for an event is usually up to an hour.
  • Using Hive and Impala for ad-hoc queries and data analysis.
  • Working on Scalding-based solution for data processing.
  • Reports run from our in-house grown OLAP-like reporting system written in Ruby.

Lessons Learned

Product Development

  • Invest in code quality.
  • Cover absolutely everything with tests.
  • Release small changes.
  • Use feature switches to deploy unfinished features to production.
  • Do not keep long running branches of code when developing something.
  • Invest in a fast release cycle.
  • Build the product mobile-first.
  • Design API very well from the very beginning, it is difficult to change it later.
  • Including sender hostname and app name in RabbitMQ messages can be a life saver.
  • Do not guess or make assumptions, do AB testing and check the data.
  • If you plan on using Redis for something big, think about sharding from very beginning.
  • Never use forked and slightly modified ruby gems if you are planning on keeping your Rails up to date.
  • Make sharing your content through social networks as easy as possible.
  • Search engine optimization is a full-time job.

Infrastructure And Operations

  • Deploy often to increase system stability. It may sound counter-intuitive at first.
  • Automate everything you can.
  • Monitor everything that can be down.
  • Network switch buffers matter.
  • Capacity planning is hard.
  • Think about HA from the start.
  • RabbitMQ cluster is not worth the effort.
  • Measure and graph everything you can: HTTP response times, Resque queue sizes, Model persistence rates, Redis response times. You cannot improve what you cannot measure.

Data Warehouse Stack

  • There’s a myriad of tools in the Hadoop ecosystem. It’s hard to pick the right one.
  • If you are writing a user defined function (UDF) for Hive it’s time to consider a non-SQL solution for data transformations.
  • The “Hadoop application” notion is vague. Oftentimes we need to glue our application components together manually.
  • Everyone writes their own workflow manager. And for a good reason.
  • Distributed system monitoring is tough. Anomaly detection and graphing helps.
  • The core Hadoop infrastructure (HDFS, YARN) is rock solid but the newer tools usually have unpleasant nuances.
  • Kafka is amazing.

source: highscalability.com