@ Alexey Kachayev | October, 2017

Who We Are • 3k+ mobile apps for events • Content management system • Social network for attendees • Leads retrieval mobile application • Marketing automation platform • Event registration system (coming soon)

In Figures • 6.5k events with 492k speakers • 3.2M mobile devices • 1.5M+ users shared 1.3M posts with 10.7M likes • Mobile API with 19K req/min at peak • 118 repos and 25+ services (micro!) • 4B+ messages in Kafka (weekly) • 230M+ documents in ElasticSearch

What Do We Use Clojure For? • For everything • No, seriously

Elaborate? • Application servers • Data pipeline • ETL jobs • Internal tools • UI • Scheduling, talking to databases, data manipulation, … you name it

Clojure at Attendify • Main & default language • 4+ years in production • 12 engineers (and hiring) • CLOC: 97K+ Clojure, 68K+ ClojureScript • It’s still a technology, not magic

Why Do We Use Clojure? • Because we like it • No, seriously

Elaborate? • Clojure = ideas + access to Java libraries and JVM - immutability, epochal time model, atoms, transformation chains, EDN, uniform domain modeling, declarative approach, runtime polymorphism with custom dispatch etc • It’s easier to use Clojure ideas in Clojure - no, seriously - “haskell in python” << “python” & “haskell in python” << “haskell” - btw, “java in clojure” >> “java” - discipline & convention don’t work, language core does

Agenda • Libraries & ecosystem • Servers & microservices • Data • Errors handling • Project setup & dev tools

Libraries & ecosystem • A lot of stuff - Clojars, Clojure Toolbox, ClojureWerkz • You still have Java - There are a lot of wrappers, but when it’s necessary… - You still have tooling: GC logs, OOM analyzers, profilers and more • You still work with Maven - lein, wagon, checkouts

Servers & Microservices • JSON-RPC and GraphQL, not REST - Might be EDN or MsgPack instead of JSON • aleph: smart wrapper for Netty - With ring & compojure • manifold, not core.async - Futures & chaining, executors, scheduling • Own library to define/use RPC - There are a few open-source libraries, like slacker and castra, tho’

Servers & Microservices (defservice “audience.fetchTimeline" :allowed-auth #{:builder} :validate-params {:profileId s/Str (s/optional-key :includeTypes) [s/Str] (s/optional-key :pageSize) s/Int} :response-format Timeline (fn [{:keys [timeline-handler]} {:keys [profileId]}] (timeline/timeline-entries …)))

Servers & Microservices (defservice “audience.fetchTimeline" :allowed-auth #{:builder} :validate-params {:profileId s/Str (s/optional-key :includeTypes) [s/Str] (s/optional-key :pageSize) s/Int} :response-format Timeline (fn [{:keys [timeline-handler]} {:keys [profileId]}] (timeline/timeline-entries …))) macro method name component(s) call params schema enforced

Servers & Microservices (rpc/call http-client {:method “audience.fetchTimeline” :params {:profileId “42”}})

Servers & Microservices (rpc/call http-client {:method “audience.fetchTimeline” :params {:profileId “42”}}) manifold.deferred component with aleph.http

Servers & Microservices • defmulti rpc/execute • defservice compiles down to defmethod • ring route to call rpc/execute • ring handlers to take care about - Logging - Errors handling - Serialization format (JSON by default)

Servers & Microservices (defservice “audience.fetchTimeline" :allowed-auth #{:builder} :validate-params {:profileId s/Str (s/optional-key :includeTypes) [s/Str] (s/optional-key :pageSize) s/Int} :response-format Timeline :dispatch-on rpc/execute (fn [{:keys [timeline-handler]} {:keys [profileId]}] (timeline/timeline-entries …))) :dispatch-on rpc/execute “magic”

Data • korma & hikari to work with PostgreSQL - Not really happy • Java API for Kafka producers/consumers - Own wrapper, but there are a few open-sourced, like kinsky & clj-kafka • carmine to work with Redis - Used to use built-in tasks/jobs queue, not now • Event sourcing with our own library - There are a few open-source libraries, like rill and cqrs-server, tho’

Data: Korma (In Theory) (defentity applications (table “application”) (pk :id) (transform #(update % :name capitalize))) (defn select-app [{:keys [conn]} app-id] (-> (select applications (db conn) (fields :name :icon) (where {:id app-id})) first))

Data: Korma (In Practice) • Connections pooling • Sophisticated queries • Serialization handling (array, hstore, jsonb) • Transactions, retries, rollbacks • java.sql.SQLException • Tables partitioning

Data: Korma (In Practice) (defn fetch-profile-with-sources* [db apikey id] (->> (models/execute-query db [(format "SELECT ps.*, ss.integration_id as source_integration_id, ss.remote_id as source_remote_id, ss.payload as source_payload, ss.is_deactivated as source_is_deactivated FROM %s ps LEFT OUTER JOIN %s ss on (ps.id = ss.profile_id) WHERE ps.apikey = ? AND ps.id = ?" (tables/route tables/profile-tbl apikey) (tables/route tables/profile-source-tbl apikey)) [apikey id]] {:raw-results? true}) (functor/fmap (fn [profiles] (->> profiles utils/aggregate-profiles (map transform-profile) first (#(dissoc % :password)))))))

Data: Korma (In Practice) (defn fetch-profile-with-sources* [db apikey id] (->> (models/execute-query db [(format "SELECT ps.*, ss.integration_id as source_integration_id, ss.remote_id as source_remote_id, ss.payload as source_payload, ss.is_deactivated as source_is_deactivated FROM %s ps LEFT OUTER JOIN %s ss on (ps.id = ss.profile_id) WHERE ps.apikey = ? AND ps.id = ?" (tables/route tables/profile-tbl apikey) (tables/route tables/profile-source-tbl apikey)) [apikey id]] {:raw-results? true}) (functor/fmap (fn [profiles] (->> profiles utils/aggregate-profiles (map transform-profile) first (#(dissoc % :password))))))) query, not DSL component not entities either manual transform partitioning

Data: Kafka Consumer • Internal library • Manage threads, subscribe/unsubscribe • Handle serialization • Exceptions, errors • Commit offsets

Data: Kafka Consumer (component/using (kafka/new-whisper {:name "pulse-audience-latest" :topic “attendify.s.a.v1" :on-message (partial pulse-audience/notify! pulse-audience-expiration-threshold pulse-audience-cache-ttl-ms) :threads 32 :kafka-config (assoc kafka-config :offset-reset "latest")}) [:redis-connector :db])

Data: Kafka Consumer (component/using (kafka/new-whisper {:name "pulse-audience-latest" :topic “attendify.s.a.v1" :on-message (partial pulse-audience/notify! pulse-audience-expiration-threshold pulse-audience-cache-ttl-ms) :threads 32 :kafka-config (assoc kafka-config :offset-reset "latest")}) [:redis-connector :db]) internal library sub/unsub consumers called on each message passed as a first arg

Errors Handling • Most of your production code - No, seriously • No good story here - Clojure gives us exceptions and nil, only • Own library for either - cats seems to be the standard here, but no one cares about monads, right? • Typing your data, not your code - schema instead of spec

Errors Handling (In Practice) (->> (pg-profile/fetch-profile-by-email* db' apikey email) (either/bind #(check-profile-nil kp apikey token email %)) (either/bind #(check-profile-deleted kp apikey token email %)) (either/bind #(check-profile-claimed-or-registered kp apikey token email %)) (either/bind #(check-valid-password kp apikey token email % password)) (either/bind #(deactivate-old-sessions db' apikey % token)) (either/bind (fn [profile] (let [session-id (or session-id (generate-session-id)) now (Timestamp/from (Instant/now))] (—>> (insert-session db' …) (either/fmap (fn [session] {…})))))))

Errors Handling (In Practice) (->> (pg-profile/fetch-profile-by-email* db' apikey email) (either/bind #(check-profile-nil kp apikey token email %)) (either/bind #(check-profile-deleted kp apikey token email %)) (either/bind #(check-profile-claimed-or-registered kp apikey token email %)) (either/bind #(check-valid-password kp apikey token email % password)) (either/bind #(deactivate-old-sessions db' apikey % token)) (either/bind (fn [profile] (let [session-id (or session-id (generate-session-id)) now (Timestamp/from (Instant/now))] (—>> (insert-session db' …) (either/fmap (fn [session] {…}))))))) errors handling

Errors Handling (In Practice) (lete [profiles (fetch-access-keys-by-events db apikey restricted-event-ids) labels (labels/fetch-labels {:db db} apikey {:type "access-key"}) events-access-keys (->> labels (filter #(some (set (:events %)) restricted-event-ids)) (map :id)) profile-ids-blacklist (->> profiles (remove #(some events-access-keys (vec (.getArray (:access_keys %))))) (map :id))] (perform-fetching-by-events db apikey event-ids profile-ids-blacklist))

Errors Handling (In Practice) (lete [profiles (fetch-access-keys-by-events db apikey restricted-event-ids) labels (labels/fetch-labels {:db db} apikey {:type "access-key"}) events-access-keys (->> labels (filter #(some (set (:events %)) restricted-event-ids)) (map :id)) profile-ids-blacklist (->> profiles (remove #(some events-access-keys (vec (.getArray (:access_keys %))))) (map :id))] (perform-fetching-by-events db apikey event-ids profile-ids-blacklist)) macro deferred[either[a’]] deferred[either[a’]]

Project Setup • Configuration is always tricky - env library, .lein-env-dev files • components - Manage (stateful) world around you - Show code dependencies • dev/user.clj - With (go) and (reset) • nREPL - Try ultra (plugin for lein)

Project Setup: component (defrecord CSVExporter [] component/Lifecycle (start [component] (if (:executor component) component (assoc component :executor (e/fixed-thread-executor threads-count)))) (stop [component] (when-let [executor (:executor component)] (.shutdownNow executor)) (assoc component :executor nil)))

Project Setup: component (defrecord CSVExporter [] component/Lifecycle (start [component] (if (:executor component) component (assoc component :executor (e/fixed-thread-executor threads-count)))) (stop [component] (when-let [executor (:executor component)] (.shutdownNow executor)) (assoc component :executor nil))) prepare cleanup

Project Setup: component (component/system-map … :csv-exporter (component/using (export/new-csv-exporter {:immediate-export-limit csv-immediate-export-limit :immediate-export-timeout csv-immediate-export-timeout :threads-count csv-export-threads-count}) [:s3-client :email-notifier :profiles-search-handler :elastic-client :settings-event-store]) … ) (e/export csv-exporter account-id other-params)

Project Setup: component (component/system-map … :csv-exporter (component/using (export/new-csv-exporter {:immediate-export-limit csv-immediate-export-limit :immediate-export-timeout csv-immediate-export-timeout :threads-count csv-export-threads-count}) [:s3-client :email-notifier :profiles-search-handler :elastic-client :settings-event-store]) … ) (e/export csv-exporter account-id other-params) component config deps convention

Project Setup: REPL $ lein repl nREPL server started on port 63248 on host 127.0.0.1 - nrepl://127.0.0.1:63248 user=> (go) :started user=> (keys @system) (:mailchimp-client :app-component :kafka-producer …) user=> (:s3-client @system) #augustine.s3.S3Client{:url …} user=> (reset) :reloading (…) :resumed user=>

Project Setup: REPL $ lein repl nREPL server started on port 63248 on host 127.0.0.1 - nrepl://127.0.0.1:63248 user=> (go) :started user=> (keys @system) (:mailchimp-client :app-component :kafka-producer …) user=> (:s3-client @system) #augustine.s3.S3Client{:url …} user=> (reset) :reloading (…) :resumed user=> try this once

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