Dmitrii Balakhonskii from Zalando in Berlin held this presentation on "Zalandos approach to microservices in Clojure" on the CLOJURE HAMBURG MEETUP in the Zalando adtech lab Office on 18th September 2017

1. Zalando’s approach
to microservices
in Clojure
Dmitrii Balakhonskii

2. 2
About me
Dmitrii Balakhonskii
• programming since 1999
• into Clojure since 2013
• in Zalando since 2015
https://github.com/dryewo

3. 3
Microservices
● relatively small
● communicating via REST
● independently deployable
● different languages,
different data storages

4. 4
Overview

5. 5
Authentication
Identity and Access Management (IAM) as a service
● gives out and rotates tokens
● checks validity of tokens

6. 6
https://github.com/zalando-stups/swagger1st
resources/api.yaml:
paths:
'/hello':
get:
operationId: my.app/get-hello
responses:
default:
description: Say hello
my/app.clj:
(defn get-hello [_ params request]
{:status 200 :body "Hello”})
RESTful API

7. 7
Load balancing

8. 8
DB Schema Migrations
https://flywaydb.org/
resources/db/migrations/V1__create_users_table.sql:
CREATE TABLE users (
id UUID PRIMARY KEY,
name TEXT NOT NULL
);
resources/db/migrations/V2__add_user_address.sql:
ALTER TABLE users
ADD COLUMN address TEXT;

9. 9
State Management
(defstate db
:start {:datasource (start-connection)}
:stop (.stop (:datasource db)}
MountStuart Sierra’s Component
(defrecord DB [datasource]
component/Lifecycle
(start [this]
(assoc this :datasource (start-connection))
(stop [this]
(when datasource
(.stop datasource))
(assoc this :datasource nil))
(defn make-db []
(map->DB {}))

10. 10
DB Access
https://www.hugsql.org/
resources/db/queries.sql:
-- :name get-users :? :*
SELECT id, address FROM users
ORDER BY name
LIMIT :limit;
users.clj:
(def-db-fns "db/queries.sql")
(get-users db {:limit 10})

11. 11
Hystrix is a library from Netflix.
https://github.com/Netflix/Hystrix/tree/master/hystrix-contrib/hystrix-clj
(defcommand cmd-get-users [db params]
(get-users db params))
(cmd-get-users db {:limit 10})
External services

12. 12
Other aspects?
https://12factor.net/
● configuration through
environment variables
● logs to STDOUT
● REPL-driven development