Lighthouse is a simple service-discovery tool for Akka.Cluster, designed to make it easier to play nice with PaaS deployments like Azure / Elastic Beanstalk / AppHarbor.
The way it works: Lighthouse runs on a static address and is not updated during deployments of your other Akka.Cluster services. You don't treat it like the rest of your services. It just stays there as a fixed entry point into the cluster while the rest of your application gets deployed, redeployed, scaled up, scaled down, and so on around it. This eliminates the complexity of traditional service discovery apparatuses by relying on Akka.Cluster's own built-in protocols to do the heavy lifting.
If you do need to make an update to Lighthouse, here are some cases where that might make sense:
- To upgrade Akka.NET itself;
- To install additional Petabridge.Cmd modules;
- To change the Akka.Remote serialization format (since that affects how Lighthouse communicates with the rest of your Akka.NET cluster); or
- To install additional monitoring or tracing tools, such as Phobos.
The easiest way to run Lighthouse is via Petabridge's official Lighthouse Docker images on Docker Hub:
docker pull petabridge/lighthouse:linux-latest
docker pull petabridge/lighthouse:windows-latest
All of these images run lighthouse on top of .NET Core 2.1 and expose the Akka.Cluster TCP endpoint on port 4053 by default. These images also come with
Petabridge.Cmd.Host installed and exposed on TCP port 9110.
Linux images also come with the
pbmclient installed as a global .NET Core tool, so you can remotely execute
pbmcommands inside the containers themselves without exposing
Petabridge.Cmd.Hostover the network.
This feature will be added to Windows container images as soon as #80 is resolved.
Lighthouse configures itself largely through the use of
Akka.Bootstrap.Docker's environment variables:
ACTORSYSTEM- the name of the
ActorSystemLighthouse will use to join the network.
CLUSTER_IP- this value will replace the
akka.remote.dot-netty.tcp.public-hostnameat runtime. If this value is not provided, we will use
CLUSTER_PORT- the port number that will be used by Akka.Remote for inbound connections.
CLUSTER_SEEDS- a comma-delimited list of seed node addresses used by Akka.Cluster. Here's an example. Lighthouse will inject it's own address into this list at startup if it's not already present.
Here's an example of running a single Lighthouse instance as a Docker container:
PS> docker run --name lighthouse1 --hostname lighthouse1 -p 4053:4053 -p 9110:9110 --env ACTORSYSTEM=webcrawler --env CLUSTER_IP=lighthouse1 --env CLUSTER_PORT=4053 --env CLUSTER_SEEDS="akka.tcp://webcrawler@lighthouse1:4053" petabridge/lighthouse:latest
Enabling Additional Akka.NET Settings
Enabling a Split Brain Resolver in Lighthouse
Here's one example of how to enable a split brain resolver in Lighthouse using these
Akka.Bootstrap.Docker environment variable substitution, using
version: '3' services: lighthouse.main: image: petabridge/lighthouse:latest hostname: lighthouse.main ports: - '9110:9110' environment: ACTORSYSTEM: "LighthouseTest" CLUSTER_PORT: 4053 CLUSTER_IP: "lighthouse.main" CLUSTER_SEEDS: "akka.tcp://LighthouseTest@lighthouse.main:4053,akka.tcp://LighthouseTest@lighthouse.second:4053,akka.tcp://LighthouseTest@lighthouse.third:4053" AKKA__CLUSTER__DOWNING_PROVIDER_CLASS: "Akka.Cluster.SplitBrainResolver, Akka.Cluster" AKKA__CLUSTER__SPLIT_BRAIN_RESOLVER__ACTIVE_STRATEGY: "keep-majority"
Running in .NET Framework
You can still run Lighthouse under .NET Framework 4.6.1 if you wish. Clone this repository and build the project. Lighthouse will run as a Topshelf Windows Service and can be installed as such.
Examples of Lighthouse in the Wild
Looking for some complete examples of how to use Lighthouse? Here's some:
Customizing Lighthouse / Avoiding Serialization Errors
When using Akka.NET with extension modules like DistributedPubSub or custom serializers (like Hyperion), serialization errors may appear in the logs because these modules are not installed and configured into Lighthouse by default. That is, required assemblies should be built into Lighthouse container.
As you may see in project file references, only
Akka.Cluster and basic
pbm modules are referenced by default, which means that if you need DistributedPubSub serializers to be discovered,
you have to build your own Lighthouse image from source, with required references included.
Basically, what you have to do is:
- Get a list of Akka.NET extension modules you are using (
Akka.Cluster.Toolsmight be the most popular, or any custom Akka.NET serialization package)
- Clone this Lighthouse repo, take Lighthouse project and add this references so that Lighthouse had all the same dependencies your Akka.Cluster nodes are using
- Build your own Docker image using Dockerfile (windows / linux) from this repository, and use your customized image instead of the default one
Workaround for DistributedPubSub
DistributedPubSub extension has
role configuration setting, which allows to select nodes that
are hosting DistributedPubSub mediators. You can use any role (let's say,
pub-sub-host) in all your cluster nodes and set
akka.cluster.pub-sub.role = "pub-sub-host" everywhere to exclude nodes that do not have this role configured.
If Lighthouse container is not configured to have this role, DistributedPubSub will not even touch it's node, which should also resolve the issue with serialization errors.