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.
- The latest version of the Giftcard App can be found on GitHub.
- Docker images for Axon Server are pushed to Docker Hub.
The Giftcard app
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
apipackage contains the (Kotlin) sourcecode of the messages and entity. They form the API (sic) of the application.
commandpackage contains the GiftCard Aggregate class, with all command- and associated eventsourcing handlers.
querypackage provides the query handlers, with their associated event handlers.
guipackage contains the Vaadin-based Web GUI.
Of these packages,
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 for Mac OSX or Linux you probably have to add "
./" in front of
Running the Giftcard app
The simplest way to run the app is by using the Spring-boot maven plugin:
However, if you have copied the jar file
giftcard-distributed-1.0.jar from the Maven
target directory to some other location, you can also start it with:
java -jar giftcard-distributed-1.0.jar
The Web GUI can be found at
If you want to activate only the
command profile, use:
java -Dspring.profiles.active=command giftcard-distributed-1.0.jar
Running the Giftcard app as micro-services
To run the Giftcard app as if it were three seperate micro-services, use the Spring-boot
spring.profiles.active option as follows:
$ java -Dspring.profiles.active=command -jar giftcard-distributed-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 (JRE versions 8 through 10 are currently supported, Java 11 still has Spring-boot related growing-pains). 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.
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-4.0-RC1.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 "
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 of 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>". For non-development scenarios, we don't recommend using Mini-Kube.
Deployment requires the use of a YAML descriptor, an 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 throught 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 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 "
... 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 ...
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'ld 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.
Environment variables for customizing the Docker image of Axon Server
axoniq/axonserver image can be customized at start by using one of the following environment variables. If no default is mentioned, leaving the environement variable unspecified will not add a line to the properties file.
This is the name the Axon Server uses for itself.
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 of the container.
This is the domain Axon Server can suffix the hostname with.
This is the port Axon Server uses for its Web GUI and REST API.
This is the gRPC port used by clients to exchange data with the server.
Setting this will enable access control, which means the clients need to pass this token with each request.
This is the directory used for storing the Events.
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 finetune in the server configuration. You can do this using an "
axonserver.properties" file. All settings have sensible defaults.
This is the name Axon Server uses for itself. The default is to use the 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.
This is the port where Axon Server will listen for HTTP requests, by default
This is the port where Axon Server will listen for gRPC requests, by default
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.
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.
Setting this to
truewill require clients to pass a 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.