I could not found any broadcast or pub/sub pattern between Reliable Services in any documentation. Did I miss anything?
My use case is , we need to notify custom event to all the SF stateful service replica in cluster if there any state change in any primary replica.
I am aware of Reliable state manager events which triggers when any change in Reliable collections.
Is there any other broadcast , pub/sub events to communicate between services replicas of the cluster ?
Thanks,
Ashish
Did you see this oss project and package? It allows pub/sub messaging between services.
Why reinvent the wheel?
Service Fabric does not contains a brokered messaging engine because:
There are lot's of options already in the market available for this.
Would make your system tight coupled with service fabric runtime.
Why not just use Service Bus Pub\Sub Topics?
If the concern is latency, why not run RabitMQ, ActiveMQ or any other messaging system as a guest executable service or maybe inside a container.
If you had this feature on SF, you would have to write your services dependent on this feature, once you start adding external dependencies, you gonna face an integration challenge to forward these events to systems outside your cluster, having to create a service listening to these events just to forward it to another queue\topic.
It will just add extra work, complexity and maintenance to your solution.
Related
I didn't find could we replace rabbitMQ/activeMQ/SQS with native kubernetes messaging queue?
or they are totally different in terms of features?
It is a totally different mechanism.
Kubernetes internal queues is not a real "queues" you can use in external applications, they are a part of internal messaging system and manage only objects which are parts of Kubernetes.
Moreover, Kubernetes doesn't provide any message queue as a service for external apps (except a situation when your app actually service one of K8s objects).
If you are not sure which service is better for your app - try to check queues.io.
That is a list of almost all available MQ engines with some highlights.
If you are referring to the Parallel Processing Using a Work Queue approach, you can technically use any queuing system, because the main logic is in the code used to get the items from the queue, Kubernetes is used only to control the parallelism.
If the idea is to use the queue algorithm used internally by kubernetes. it is not exposed as a a service for external applications, you would have to copy the code and implement in you application.
My company is interested in using a stand-alone Service Fabric cluster to manage communications with robots. In our scenario, each robot would host its own rosbridge server, and our Service Fabric application would maintain WebSocket clients to each robot. I envision a stateful service partitioned along device ids which opens connections on startup. It should monitor connection health via heartbeats, pass messages from the robots to some protocol gateway service, and listen to other services for messages to pass to the robots.
I have not seen discussion of this style of external communications in the Service Fabric documentation - I cannot tell if this is because:
There are no special considerations for managing WebSockets (or any two-way network protocol) this way from Service Fabric. I've seen no discussion of restrictions and see no reason, conceptually, why I can't do this. I originally thought replication would be problematic (duplicate messages?), but since only one replica can be primary at any time this appears to be a non-issue.
Service Fabric is not well-suited to bi-directional communication with external devices
I would appreciate some guidance on whether this architecture is feasible. If not, discussion on why it won't work will be helpful. General discussion of limitations around bi-directional communication between Service Fabric services and external devices is welcome. I would prefer if we could keep discussion to stand-alone clusters - we have no plans to use Azure services at this time.
Any particular reason you want SF to host the client and not the other way around?
Doing the way you suggest, I think you will face big challenges to make SF find these devices on your network and keep track of them, for example, Firewall, IPs, NAT, planned maintenance, failures, connection issues, unless you are planning to do it by hand.
From the brief description I saw in the docs your provided about rosbridge server, I could understand that you have to host it on a Server(like you would with a service fabric service) and your devices would connect to it, in this case, your devices would have installed the ROS to make this communication.
Regarding your concerns about the communication, service fabric services are just executable programs you would normally run on your local machine, if it works there will likely work on service fabric environment on premise, the only extra care you have to worry is the external access to the cluster(if in azure or network configurations) and service discovery.
In my point of view, you should use SF as the central point of communication, and each device would connect to SF services.
The other approach would be using Azure IoT Hub to bridge the communication between both. There is a nice Iot Hub + Service Fabric Sample that might be suitable for your needs.
Because you want to avoid Azure, you could in this case replace IoT Hub with another messaging platform or implement the rosbridge in your service to handle the calls.
I hope I understood everything right.
About the obstacles:
I think the major issue here is that bi-directional connection can be established between service replica and the robot.
This has two major problems:
Only primary replica has write access - i.e. only one replica would be able to modify state. This issue hence could be mitigated by creating a separate partition for each robot (but please remember that you can't change partition count after the service was created) or by creating a separate service instance for each robot (this would allow you to dynamically add or remove robots but would require additional logic related to service discoverability).
The replica can be shutdown (terminated), moved to another node (shutdown and start of new replica) or even demoted (the primary replica get's demoted to secondary and another secondary replica get's promoted to primary) by various reasons. So the service code and robot communication code should be able to handle this.
About WebSockets
This looks possible by implementing custom ICommunicationListener and other things using WebSockets.
Consider a scenario where I have a watcher-service which is registered in consul. In this watcher service, I want to trigger some emails based on the behaviour of other services i.e. when other services are up, when a new service is added and when a running service is down.
My question is how can I subscribe to the events of other services.
One way I got is to use a scheduler and keep hitting consulClient.agentServices but this seems not an optimal way. I am hoping that I should be able to add a listener / watcher which invoke method which inturn tells watcher-service which service is down/added.
Looking for solutions which are more specific to spring cloud consul, but all hints are warmly welcome.
I want to know if it is possible to run kafka as a cloud-native application, and can I create a kafka cluster as a service on Pivotal Web Services. I don't want only client integration, I want to run the kafka cluster/service itself?
Thanks,
Anil
I can point you at a few starting points, there would be some work involved to go from those starting points to something fully functional.
One option is to deploy the kafka cluster on Cloud Foundry (e.g. Pivotal Web Services) using docker images. Spotify has Dockerized kafka and kafka-proxy (including Zookeeper). One thing to keep in mind is that PWS currently doesn't support apps with persistence (although this work is starting) so if you were to go this route right now, you would lose the data in kafka when the application is rolled. Looking at that Spotify repo, it looks like the docker images are generally run without any mounted volumes, so this persistence-less kafka seems like it may be a valid use case (I don't know enough about kafka to say).
The other option is to deploy kafka directly on some IaaS (e.g. AWS) using BOSH. BOSH can be hard if you're seeing it for the first time, but it is the ideal way to deploy any distributed software that you want running on VMs. You will also be able to have persistent volumes attached to your kafka VMs if necessary. Here is a kafka BOSH release which may work.
Once you have your cluster running, you have two ways to integrate your Cloud Foundry applications with it. The simplest is just to provide it to your applications as a "user-provided service", which lets you flow kafka cluster access info to your apps. The alternative would to put a service broker in front of your cluster, which would be especially useful if you have many different people who will be pushing apps that need to talk to the kafka cluster. Rather than you having to manually tell people the access info each time, they can do something simple like cf bind-service SOME_APP YOUR_KAFKA_SERVICE. Here is a kafka service broker along with more info about service brokers in general.
According to the 12-factor app description (https://12factor.net/processes), Kafka should not run as an application on top of Cloud Foundry:
Twelve-factor processes are stateless and share-nothing. Any data that needs to persist must be stored in a stateful backing service, typically a database.
Kafka is often considered a "distributed commit log" and as such carries a large amount of state. Many companies use it to keep all events flowing through their distributed system of micro services for a long (sometimes unlimited) amount of time.
Therefore I would strongly recommend to go for the second option in the accepted answer: Kafka topics should be bound to your applications in the form of stateful services.
I'm fairly new to Akka and new to distributed programming in general. Using Akka's Mist component, I've created supervised actors to handle HTTP requests asynchronously. Everything is currently running on one physical machine with local actors. What I don't understand is how to build a truly fault-tolerant system with more than one box. As stated in the Akka docs:
Also, you (usually) need to know if one box is down and/or the service you are talking to on the other box is down. Here actor supervision/linking is a critical tool for not only monitoring the health of remote services, but to actually manage the service, do something about the problem if the actor or node is down. Such as restarting actors on the same node or on another node.
How do I do this? I'm looking for an example or pointers on how to begin making my application distributed. Other services in our group use Apache gateways in front of multiple Tomcat instances, so the event of a Tomcat server going down is transparent to the user. I'm deploying my service to the Akka microkernel and need to achieve a similar level of high availability across more than one physical box.
I'm using Akka 1.1.3.
Remote supervision works only with client-managed remote actors for the Akka 1.x series.
Akka 2.0 that is currently under development will support transparent clustering, cluster-wide supervision and cluster-wide lifecycle monitoring.
You might consider putting an HTTP load balancer in front of Akka Microkernel instances running Mist, this would match what your group does with 'Apache gateways'.
Another approach would be to expose remote actors on a number of instances and then use Akka's LoadBalancer or Actor Pool to send messages around, see here
The second approach is a bit of a pain if you have a dynamic pool of machines, because the pool of devices wants to be specified programatically. Akka 2.0 addresses this with cluster support that is setup in the akka.conf file.
As far as the release date of 2.0, for what its worth 1.2 was just recently released on 2011-Sept-19.