Clojure project in the field

Transcript

1. Clojure chez Electre
   Retour d’expérience
   

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2. Contexte Electre produit un service de recherche
   dans une base d’œuvres
   bibliographique (1,3M) mais également
   musicale, cinématographique et jeux
   vidéos. Ce service est utilisé par les
   bibliothèques, les libraires et e-
   commerçant avec environ 2M de notices
   et 4M de requêtes par jour.
   

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4. 4
   Hexagonal
   Architecture
   SPA
   ClojureScript
   Re-frame
   PostgreSQL
   Google Cloud
   Solr
   Kafka
   Keycloak
   TDD
   Vault
   Architecture Decision Records
   Clojure Yada / Mount / HugSQL / Clojure.spec
   BDD / Scenari
   Command /
   Query / Event
   REST API
   BigQuery
   Tools.deps
   Struct. Logging
   Kub. / Docker
   EFK
   Prometheus
   Gitlab CI
   Shadow-cljs
   Cloud Storage
   (~S3)
   DDD
   Monorepo
   

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5. 5
   « When you start modeling events, it
   forces you to think about the behavior of
   the system. As opposed to thinking about
   the structure of the system »
   Greg Young
   

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6. MAKE COMMAND, QUERY
   AND EVENT
   FIRST CLASS CONCEPTS
   

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7. EVENT
   FACTS,
   APPEND-ONLY
   Past Future
   Now
   COMMAND
   INTENTION,
   SUCCEED OR FAIL
   QUERY
   CURRENT STATE
   

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8. EVENT
   An Event represents a fact about the domain from the past
   Events are raised on every state transition that acknowledged the new fact as data in our
   system
   Event can reference the command or query identifier that trigger it
   Events can be ignored, but can’t be retracted or deleted, only a new event can invalidate
   a previous one
   Events are named with a past participle
   There are internal and external event:
   § Internal Events: the ones we raised and control in our Bounded Context
   § External Events: the ones from other upstream BC we subscribed to
   « Something happened that domain
   experts care about » E.Evans
   

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9. COMMAND
   A command represents an intention
   The result of a command can be either success or failure, the result is an
   event
   In case of success, state change(s) must have occured somewhere
   (otherwise nothing happened)
   Commands are named with a verb, in present tense of infinitive and a
   nominal group coming from the domain (entity of aggregate type)
   « A Command is a request
   made to do something »
   

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10. QUERY
    A query ask a system for data in a specific model
    Query never change the state of the system (they are idempotent)
    The query processing is often synchronous
    The query contains fields with some value to match for or an identifier
    Query can results in success or failure (not found) and long results can be
    paginated
    Queries are named with: “get” something (with identifier as arguments) or
    “find” something (with values to match as arguments)
    « A Query is a request asking to
    retrieve some data about the
    current state of a system »
    

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11. Submitted Paid …
    Command
    Event
    Order State
    § Customer Details
    § Order Lines (product + qty)
    § Shipping Info
    § Payment
    Receipt
    § …
    Submit Order Pay Order …
    Order
    Submitted
    Order Paid …
    

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12. EVENT-DRIVEN SYSTEM INTERFACE
    System
    Command
    Event
    Command
    Event
    INTERFACE OF THE SYSTEM AS THE SET OF ACCEPTED
    COMMANDS & QUERIES AND PUBLISHED EVENTS
    Query
    Query
    

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13. Event Bus
    Event-Driven
    Architecture &
    Backend
    Software
    Architecture
    Command Query
    Internal
    Event
    Domain
    Logic
    Interface of the Backend System
    Each Command will trigger a state transition
    of the targeted Entity
    Event
    State
    Transition
    publish subscribe
    

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14. Hexagonal
    Architecture
    APPLICATION
    LOGIC
    DOMAIN
    LOGIC
    INFRASTRUCTURE
    LOGIC
    

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15. Event-Driven
    Architecture
    & Software
    Architecture Frontend
    Backend
    Command Query
    Internal
    Event
    Command Query
    Internal
    Event
    POST GET
    SSE or
    Websocket
    Hexagonal Architecture on the Backend
    Unidirectional Architecture on the Frontend
    REST API
    

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16. WHY CLOJURE?
    

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17. Why
    Clojure?
    Data processing and Frontend app with re-frame
    are the two main reasons
    Benefits
    § Simple, powerful and make people productive
    § Best language for Data Processing
    § Hosted (JVM / JS) easy interop with common
    infrastructure (Solr, Kafka, Keycloak, DBs,
    etc.)
    § Recruitment
    

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18. Why
    Clojure?
    Drawbacks
    § Recruitment
    § Decisions are to be made, nothing is served
    on a plate (like Spring, .Net) but allows great
    freedom and power
    

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19. Clojure
    Libraries:
    buy or
    build?
    For each library: Do I “buy” an existing one
    or build a closely fitted one?
    § Example with Solr
    § Example with Keycloak
    § Example with Kafka
    § Example with Scenari (BDD execution lib)
    

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20. Tools.Deps Love the simplicity and composability
    Not as rich and mature as Leiningen
    Shell scripts as “interface” for the developer.
    Minimal interface:
    build.sh / run.sh
    test.sh / release.sh
    “Metav” lib for version and release
    management
    

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21. Rampup
    for
    beginners?
    Easy
    Difficult when the project is starting as a
    lot of decisions are not made
    

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22. HOW TO SELL CLOJURE?
    

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23. Selling
    Clojure to
    managers
    Quick answer: it’s not Clojure
    A mix of trust (hence people), risk and cost.
    The only question is: can we deliver? For how
    much?
    In a polyglot world: platform is first, language
    is second.
    Infrastructure choice is costly, hexagonal
    architecture makes the investment in the
    domain logic perennial.
    

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24. TAKEAWAYS
    Clojure is fun and amazing!
    The interop is easy and the greatest benefit
    Immutability makes everything simpler and easier to reason
    about, always in flow
    The challenges are in the product and domain design, hence
    the organization and people, not the technology
    

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25. ELECTRE IS RECRUITING J
    JOBS.ELECTRE.COM
    

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