Lagom Workshop BarcelonaJUG 2017-06-08

Ignasi Marimon-Clos - @ignasi35
(based on slides by Markus Jura - @markusjura)
Microservices “Just Right”

Lagom - [lah-gome]
Adequate, sufficient, just right

• Overview
• Developer experience
• Service API
• Persistence & Clustering
• Running in production
TOC

• Reactive
• Built-in resiliency & failure handling patterns
• Developer experience
• No setup of external services
• Intra-service communication just works
• Services automatically reload on code change
• Takes you through to production deployment
Why Lagom?

• Java 8
• Play 2.5
• Akka 2.4 (Clustering, Streams, Persistence)
• Cassandra (default data store)
• Jackson (JSON serialization)
• Guice (DI)
Under the hood

• Ocado rip-off
• BasketService: CreateBasket, AddItem, RemoveItem
• InventoryService: AddItem, ProvisionItem, ReserveItem, PickUpItem
• OrderService: PlaceOrder, CompleteOrder, FailOrder
• DeliveryService: DeliverOrder
Today’s workshop

BasketService
OrderService
InventoryService
DeliveryService

$ sbt runAll
$ mvn lagom:runAll

Service definition
public interface BasketService extends Service {
@Override
default Descriptor descriptor() {
return named("basketservice").withCalls(
namedCall("/api/baskets", this::createBasket)
)
}
ServiceCall<Basket, String> createBasket();
}

Service definition
public interface BasketService extends Service {
@Override
return named("basketservice").withCalls(
restCall(Method.POST,
”/api/baskets”,this::createBasket)
)
}
ServiceCall<Basket, String> createBasket();
}

Each service definition is split into two sbt projects: api &
impl
Anatomy Lagom project
my-lagom-system ! Project root 
# helloworld-api ! helloworld api project 
# helloworld-impl ! helloworld implementation project 
# project ! sbt configuration files 
# plugins.sbt ! sbt plugins 
# build.sbt ! Your project build file

Service definition
public interface FriendService extends Service {
@Override
return named("friendservice").withCalls(
restCall(Method.POST,
”/api/users”,this::createUser)
)
}
ServiceCall<User, String> createUser();
}

Service definition
@Override
pathCall(”/api/users”,this::createUser)
)
}
}

Service definition
// this source is placed in your api project
@Override
namedCall(”createUser", this::createUser)
)
}
}

Service definition
@Override
call(this::createUser)
)
}
}

$ sbt runAll
[info] Loading project definition from /Users/ignasi/workshop/hello/project
[info] Set current project to hello-workshop (in build file:/Users/ignasi/workshop/hello/)
[info] Updating {file:/Users/ignasi/workshop/hello/}lagom-internal-meta-project-kafka...
[info] Resolving jline#jline;2.12.1 ...
[info] Done updating.
[info] Starting Kafka
[info] Updating {file:/Users/ignasi/workshop/hello/}lagom-internal-meta-project-cassandra...
[info] Resolving com.google.guava#guava;18.0 ...
SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
SLF4J: Defaulting to no-operation (NOP) logger implementation
[info] Starting Cassandra
..........
[info] Cassandra server running at 127.0.0.1:4000
[info] Updating {file:/Users/ignasi/workshop/hello/}lagom-internal-meta-project-service-locator...
[info] Service locator is running at http://localhost:8000
[info] Service gateway is running at http://localhost:9000
[info] Compiling 3 Java sources to /Users/ignasi/workshop/hello/hello-api/target/scala-2.11/classes...
[info] Compiling 1 Java source to /Users/ignasi/workshop/hello/hello-stream-api/target/scala-2.11/classes...
[info] Compiling 4 Java sources to /Users/ignasi/workshop/hello/hello-stream-impl/target/scala-2.11/classes...
[info] Compiling 6 Java sources to /Users/ignasi/workshop/hello/hello-impl/target/scala-2.11/classes...
[warn] o.a.k.c.NetworkClient - Error while fetching metadata with correlation id 1 : {hello-
events=LEADER_NOT_AVAILABLE}
[warn] o.a.k.c.NetworkClient - Error while fetching metadata with correlation id 2 : {hello-
events=LEADER_NOT_AVAILABLE}
[info] Service hello-impl listening for HTTP on 0:0:0:0:0:0:0:0:57797
[info] Service hello-stream-impl listening for HTTP on 0:0:0:0:0:0:0:0:58322
[info] (Services started, press enter to stop and go back to the console...)

curl http://localhost:9000/api/hello/Alice

Service definition
@Override
namedCall(”createUsers", this::createUsers)
)
}
ServiceCall< Source<User,…> , …> createUsers();
}

$ git clone
https://github.com/ignasi35/lagom-java-workshop.git
ex001-start

Exercise
• Create service descriptor for Basket Service
ex001-start

Service definition
public interface SearchService extends Service {
@Override
return named("search").withCalls(
pathCall(
”/api/search?pageNo&pageSize“,
this::search)
)
}
ServiceCall<SearchRequest, PageSeq<Result>>
search(int pageNo, int pageSize);
}

… pet/findByStatus”:{“get":{"tags":["pet"],"summary":"Finds Pets by
status","description":"Multiple status values can be provided with comma separated
strings","operationId":"findPetsByStatus","produces":["application/xml","application/
json"],"parameters":[{"name":"status","in":"query","description":"Status values that need to
be considered for filter","required":true,"type":"array","items":{"type":"string","enum":
["available","pending","sold"],"default":"available"},"collectionFormat":"multi"}],"responses
":{"200":{"description":"successful operation","schema":{"type":"array","items":{"$ref":"#/
definitions/Pet"}}},"400":{"description":"Invalid status value"}},"security":
[{"petstore_auth":["write:pets","read:pets"]}]}},"/pet/findByTags":{"get":{"tags":
["pet"],"summary":"Finds Pets by tags","description":"Muliple tags can be provided with comma
separated strings. Use tag1, tag2, tag3 for
testing.","operationId":"findPetsByTags","produces":["application/xml","application/
json"],"parameters":[{"name":"tags","in":"query","description":"Tags to filter
by","required":true,"type":"array","items":
{"type":"string"},"collectionFormat":"multi"}],"responses":{"200":{"description":"successful
operation","schema":{"type":"array","items":{"$ref":"#/definitions/Pet"}}},"400":
{"description":"Invalid tag value"}},"security":[{"petstore_auth":
["write:pets","read:pets"]}],"deprecated":true}},"/pet/{petId}":{"get":{"tags":
["pet"],"summary":"Find pet by ID","description":"Returns a single
pet","operationId":"getPetById","produces":["application/xml","application/
json"],"parameters":[{"name":"petId","in":"path","description":"ID of pet to
return","required":true,"type":"integer","format":"int64"}],"responses":{"200":
{"description":"successful operation","schema":{"$ref":"#/definitions/Pet"}},"400":
{"description":"Invalid ID supplied”},…

Service call explained
public interface ServiceCall<Request, Response> {
CompletionStage<Response> invoke(Request request)
}
• ServiceCall is invoked when consuming a service
• JSON is the default serialization format for request/response
messages
• There are two kinds of request/response messages
• Strict
• Streamed
SAM

Strict Messages
namedCall("/api/users", this::createUser)
)
}
Strict messages are buffered into memory

Streamed Messages
return named("activityservice").withCalls(
pathCall("/activity/:userId", this::stream)
)
}
ServiceCall<NotUsed, Source<Tweet, ?>> stream(String userId);
• Streamed message is of type Source (Akka streams API)
• Back-pressured, asynchronous handling of messages
• Lagom selects transport protocol (currently WebSockets)

Remember the Service definition?
@Override
namedCall("/api/users", this::createUser)
)
}
}

Service implementation
import com.lightbend.lagom.javadsl.api.*;
import akka.NotUsed;
import static java.util.concurrent.CompletableFuture.completedFuture;
@Override
public ServiceCall<User, String> createUser() {
return request -> completedFuture("Created user");
}

Exercise
• Implement deleteItem
ex002-startEx001-end

Intra-service communication
public class MyModule
extends AbstractModule // Guice
implements ServiceGuiceSupport { // Lagom
protected void configure() {
bindClient(FriendService.class);
…
}

public class LikesSrvcImpl implements LikesService {
private final friendService;
@Inject
public LikesSrvcImpl(FriendService friendSrvc) {
this.friendService = friendSrvc;
}
…

@Override
public ServiceCall<…,…> like(String id) {
return request -> {
CompletionStage<String> userId =
friendService.createUser(user).invoke()
return userId;
}
}

Circuit breakers
• Circuit breaker is used to provide stability and prevent cascading
failures
• Services calls interacting with Lagom services are using circuit
breakers by default
• Circuit breakers can be configured
• Each service call can have a separate circuit breaker

Lagom Persistence
Lagom
Persistence
CQRS Event
Sourcing
implements Using

Commands
Queries
???
Data
Info

Events = g(Staten, Command)
Staten+1 = h(Staten, Event)

List<Event> g(State, Command)
State h(State, Event)

(State, Command) -> List<Event>
(State, Event) -> State

State -> Command -> List<Event>
State -> Event -> State

State -> Command -> List<Event>
State -> Event -> State
Info = f(data)

Commands
Queries
Data
Info
Info

Journal
Snapshots
Projections
Write-side
Read-side

Exercise
• Implement the InventoryIncreased command handling
ex003-start

Persistent Entities
• Persistent Entity corresponds to an
Aggregate Root (DDD)
• Persistent Entities receive commands
• Triggered by a command, Persistent
Entities will change their state
• Example: CreateBasket, AddItem(“apple”,
3), RemoveItem(“apple”, 7), AddItem(“apple”,
5), Checkout
FriendService
Peter
Bob
Alice

Lagom Cluster
• Lagom allows you to scale
out by forming a cluster of
nodes
• Nodes can be added and
removed dynamically
Node A
Node B
Node C
Node D
join

Lagom Cluster
• Lagom allows you to scale
out by distributing your
Persistent Entities in the
cluster
Node A Node B
Node C
X
Bob
Alice
Z
X
Steve
Paul
Peter

Lagom Cluster
• We have now moved from
a CRUD approach to a
Memory Image approach
• We keep all* our data in
memory!
• See http://
martinfowler.com/bliki/
MemoryImage.html
 
(*) or a working set, actors can be
passivated and activated as needed
Node A Node B
Node C
X
Bob
Alice
Z
X
Steve
Paul
Peter

Lagom Persistence
• But how does our data
survive a system crash?
• We log all the state
changes!
• Persistent Entities are
recreated on another node
and all state changes are
replayed
Node A Node B
Node C
X
Bob
Alice
Z
X
Y
Paul
Peter

Lagom Persistence
Node A
Node C
X
Bob
Alice
Paul
Peter Steve

Exercise
• Fix the InventoryDecreased command handling and
write a test to prevent bug regressions
ex004-start

Event sourcing: Storing deltas
• Every state change is materialized in an Event
• All events are stored in an Event Log
• Current state is constructed by replaying all events

Event Sourcing: Benefits
• Bullet-proof auditing and historical tracing
• Support future ways of looking at data
• No object-relational impedance mismatch
• Performance and scalability
• Testability

• Keep all data in memory
• Optional: Only working set, by using passivation/activation
• Store all state changes as events
• Replay all events to re-create the state
• Optional: Start from snapshot
• Scale out with Lagom Cluster and scalable data store
Event Sourcing with Lagom Persistence

Read-Side
UserCreated(Alice)
FriendAdded(Bob)
FriendAdded(Peter)
FOLLOWERS
userid followedby
Bob Alice
Bob X
Bob Y
Peter Alice

• Derived from event log
• Can be discarded and re-created
• The “book of record” is the event log
• Can be scaled out by creating copies - it’s read only
Read-Side

Consistency
FOLLOWERS
userid followedby
Bob Alice
Bob X
Bob Y
Peter Alice
Data Store
(e.g. Cassandra Cluster)
Alice1 - Persistent
Entity
2 - Journal / Event Log
3 - Read Side

Consistency
Alice
• Persistent Entities define an
Aggregate root
• Aggregate Root is the Transactional
Boundary
• Strong consistency within an
Aggregate Root
• Commands are executed sequentially
on the latest state
• No limit to scalability
1 - Persistent
Entity

Consistency
• Depending on implementation and
configuration
• Popular choice: Casssandra
• “Tunable consistency”
• Use of quorums ensures consistencyData Store
(e.g. Cassandra Cluster)
2 - Journal / Event Log

Consistency
• Will not be updated immediately, but
deferred
• Not much different from queries in
interactive applicationsFOLLOWERS
userid followedby
Bob Alice
Bob X
Bob Y
Peter Alice
3 - Read Side

What if I don’t want to use Event Sourcing?
• Don’t use Lagom Persistence
• You can use any data store
• Beware of blocking APIs (JDBC)

Journal
Snapshots
Write-side
Read-side

Exercise
• Consume the topic where BasketService emits events to
generate the InventoryDecreased commands into
InventoryEntity
ex005-start

• sbt-native packager produces several packages
• ZIP
• Docker
• RPM
• ConductR bundle
Packaging

• Infrastructure need to support Akka clustering
• Deployment tool
• Need to implement Lagom service locator interface
• Should handle node failure scenarios
Production considerations

• Akka Cluster support
• Service locator
• Consolidated logging
• Restart services automatically
• Handling network failures
• Rolling updates
• Monitoring support
ConductR

• Getting started: lightbend.com/lagom
• Examples: lightbend.com/activator/templates
• Contribute: https://github.com/lagom
• Communicate:
• https://groups.google.com/forum/#!forum/lagom-framework
• https://gitter.im/lagom/lagom
• Lightbend Proof of Concept Program: lightbend.com/company/
contact
Try it out

Read this book
https://www.lightbend.com/reactive-
microservices-architecture
(free, registration required)

Lagom Workshop BarcelonaJUG 2017-06-08

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