Getting started with Axon

This Axon Framework demo application focuses around a simple giftcard domain, designed to show various aspects of the framework. The app can be run in various modes, using Spring-boot Profiles: by selecting a specific profile, only the corresponding parts of the app will be active. Select none, and the default behaviour is activated, which activates everything. This way you can experiment with Axon in a (structured) monolith as well as in micro-services.

Where to find more information:

• The Axon Reference Guide is definitive guide on the Axon Framework and Axon Server.
• Visit www.axoniq.io to find out about AxonIQ, the team behind the Axon Framework and Server.
• Subscribe to the AxonIQ YouTube channel to get the latest Webinars, announcements, and customer stories.
• To start a fresh Axon Application, you can go to start.axoniq.io.
• Additional information may be gained by following some of AxonIQ's courses on the AxonIQ Academy.
• The latest version of the Giftcard App can be found on GitHub.
• Docker images for Axon Server are pushed to Docker Hub.
• If there are any Axon related questions remaining, you can always go to the forum.

The Giftcard app

Background story

See the wikipedia article for a basic definition of gift cards. Essentially, there are just two events in the life cycle of a gift card:

• They get issued: a new gift card gets created with some amount of money stored.
• They get redeemed: all or part of the monetary value stored on the gift card is used to purchase something.

Structure of the App

The Giftcard application is split into four parts, using four sub-packages of io.axoniq.demo.giftcard:

• The api package contains the (Kotlin) sourcecode of the messages and entity. They form the API (sic) of the application.
• The command package contains the GiftCard Aggregate class, with all command- and associated eventsourcing handlers.
• The query package provides the query handlers, with their associated event handlers.
• The gui package contains the Vaadin-based Web GUI.

Of these packages, command, query, and gui are also configured as profiles.

Building the Giftcard app from the sources

To build the demo app, simply run the provided Maven wrapper:

./mvnw clean package

Note that the Giftcard app expects JDK 11 to be used.

Running the Giftcard app

The simplest way to run the app is by using the Spring-boot maven plugin:

./mvnw spring-boot:run

However, if you have copied the jar file giftcard-demo-1.0.jar from the Maven target directory to some other location, you can also start it with:

java -jar giftcard-demo-1.0.jar

The Web GUI can be found at http://localhost:8080.

If you want to activate only the command profile, use:

java -Dspring.profiles.active=command giftcard-demo-1.0.jar

Idem for query and gui.

Running the Giftcard app as microservices

To run the Giftcard app as if it were three separate microservices, use the Spring-boot spring.profiles.active option as follows:

$ java -Dspring.profiles.active=command -jar giftcard-demo-1.0.jar

This will start only the command part. To complete the app, open two other command shells, and start one with profile query, and the last one with gui. Again you can open the Web GUI at http://localhost:8080. The three parts of the application work together through the running instance of the Axon Server, which distributes the Commands, Queries, and Events.

Running Axon Server

By default, the Axon Framework is configured to expect a running Axon Server instance, and it will complain if the server is not found. To run Axon Server, you'll need a Java runtime.
A copy of the server JAR file has been provided in the demo package. You can run it locally, in a Docker container (including Kubernetes or even Mini-kube), or on a separate server.

The section below give a fair description on how to run Axon Server for this sample project. If you are looking for more in depth information on the subject, we recommend this three-part blog series:

1. Running Axon Server - Going from local developer install to full-featured cluster in the cloud
2. Running Axon Server in Docker - Continuing from local developer install to containerized
3. Running Axon Server in a Virtual Machine

Running Axon Server locally

To run Axon Server locally, all you need to do is put the server JAR file in the directory where you want it to live, and start it using:

java -jar axonserver-4.5-9.jar

You will see that it creates a subdirectory data where it will store its information.

Running Axon Server in a Docker container

To run Axon Server in Docker you can use the image provided on Docker Hub:

$ docker run -d --name my-axon-server -p 8024:8024 -p 8124:8124 axoniq/axonserver
...some container id...
$

WARNING This is not a supported image for production purposes. Please use with caution.

If you want to run the clients in Docker containers as well, and are not using something like Kubernetes, use the "--hostname" option of the docker command to set a useful name like "axonserver", and pass the AXONSERVER_HOSTNAME environment variable to adjust the properties accordingly:

$ docker run -d --name my-axon-server -p 8024:8024 -p 8124:8124 --hostname axonserver -e AXONSERVER_HOSTNAME=axonserver axoniq/axonserver

When you start the client containers, you can now use "--link axonserver" to provide them with the correct DNS entry. The Axon Server Connector looks at the "axon.axonserver.servers" property to determine where Axon Server lives, so don't forget to set it to "axonserver".

Running Axon Server in Kubernetes and Mini-Kube

WARNING: Although you can get a pretty functional cluster running locally using Mini-Kube, you can run into trouble when you want to let it serve clients outside the cluster. Mini-Kube can provide access to HTTP servers running in the cluster, for other protocols you have to run a special protocol-agnostic proxy like you can with "kubectl port-forward <pod-name> <port-number>". Thus, for non-development scenarios, we don't recommend using Mini-Kube.

Deployment requires the use of a YAML descriptor, a working example of which can be found in the "kubernetes" directory. To run it, use the following commands in a separate window:

$ kubectl apply -f kubernetes/axonserver.yaml
statefulset.apps "axonserver" created
service "axonserver-gui" created
service "axonserver" created
$ kubectl port-forward axonserver-0 8124
Forwarding from 127.0.0.1:8124 -> 8124
Forwarding from [::1]:8124 -> 8124

You can now run the Giftcard app, which will connect through the proxied gRPC port. To see the Axon Server Web GUI, use "minikube service --url axonserver-gui" to obtain the URL for your browser. Actually, if you leave out the "--url", minikube will open the GUI in your default browser for you.

To clean up the deployment, use:

$ kubectl delete sts axonserver
statefulset.apps "axonserver" deleted
$ kubectl delete svc axonserver
service "axonserver" deleted
$ kubectl delete svc axonserver-gui
service "axonserver-gui" deleted

If you're using a 'real' Kubernetes cluster, you'll naturally not want to use "localhost" as hostname for Axon Server, so you need to add three lines to the container spec to specify the "AXONSERVER_HOSTNAME" setting:

...
      containers:
      - name: axonserver
        image: axoniq/axonserver
        imagePullPolicy: Always
        ports:
        - name: grpc
          containerPort: 8124
          protocol: TCP
        - name: gui
          containerPort: 8024
          protocol: TCP
        readinessProbe:
          httpGet:
            port: 8024
            path: /actuator/health
          initialDelaySeconds: 5
          periodSeconds: 5
          timeoutSeconds: 1
        env:
        - name: AXONSERVER_HOSTNAME
          value: axonserver
---
apiVersion: v1
kind: Service
...

Use "axonserver" (as that is the name of the Kubernetes service) if you're going to deploy the client next to the server in the cluster, which is what you'd probably want. Running the client outside the cluster, with Axon Server inside, entails extra work to enable and secure this, and is definitely beyond the scope of this example.

Configuring Axon Server

Axon Server uses sensible defaults for all of its settings, so it will actually run fine without any further configuration. However, if you want to make some changes, below are the most common options. For an exhaustive list, we recommend checking out the Configuration section of the Reference Guide.

Environment variables for customizing the Docker image of Axon Server

The axoniq/axonserver image can be customized at start by using one of the following environment variables. If no default is mentioned, leaving the environment variable unspecified will not add a line to the properties file.

• AXONSERVER_NAME

  This is the name the Axon Server uses for itself.

• AXONSERVER_HOSTNAME

  This is the hostname Axon Server communicates to the client as its contact point. Default is "localhost", because Docker generates a random name that is not resolvable outside the container.

• AXONSERVER_DOMAIN

  This is the domain Axon Server can suffix the hostname with.

• AXONSERVER_HTTP_PORT

  This is the port Axon Server uses for its Web GUI and REST API.

• AXONSERVER_GRPC_PORT

  This is the gRPC port used by clients to exchange data with the server.

• AXONSERVER_TOKEN

  Setting this will enable access control, which means the clients need to pass this token with each request.

• AXONSERVER_EVENTSTORE

  This is the directory used for storing the Events.

• AXONSERVER_CONTROLDB

  This is where Axon Server stores information of clients and what types of messages they are interested in.

Axon Server configuration

There are a number of things you can fine-tune in the server configuration. You can do this using an "axonserver.properties" file. All settings have sensible defaults.

• axoniq.axonserver.name

  This is the name Axon Server uses for itself. The default is to use the hostname.

• axoniq.axonserver.hostname

  This is the hostname clients will use to connect to the server. Note that an IP address can be used if the name cannot be resolved through DNS. The default value is the actual hostname reported by the OS.

• server.port

  This is the port where Axon Server will listen for HTTP requests, by default 8024.

• axoniq.axonserver.port

  This is the port where Axon Server will listen for gRPC requests, by default 8124.

• axoniq.axonserver.event.storage

  This setting determines where event messages are stored, so make sure there is enough diskspace here. Losing this data means losing your Events-sourced Aggregates' state! Conversely, if you want a quick way to start from scratch, here's where to clean.

• axoniq.axonserver.controldb-path

  This setting determines where the message hub stores its information. Losing this data will affect Axon Server's ability to determine which applications are connected, and what types of messages they are interested in.

• axoniq.axonserver.accesscontrol.enabled

  Setting this to true will require clients to pass a token.

• axoniq.axonserver.accesscontrol.token

  This is the token used for access control.

The Axon Server HTTP server

Axon Server provides two servers; one serving HTTP requests, the other gRPC. By default, these use ports 8024 and 8124 respectively, but you can change these in the settings.

The HTTP server has in its root context a management Web GUI, a health indicator is available at /actuator/health, and the REST API at /v1. The API's Swagger endpoint finally, is available at /swagger-ui.html, and gives the documentation on the REST API.