I am planning to use vaultTrack method to track the changes in state object.Once I capture the events at client level am planning to store those data in offline DB or invoke another API. Will there will be any challenge in this implementation. As per my understanding RPC client library will be listening all the time for state changes and also it handles the incoming RPC calls from external parties . Will it slow down the performance. How exactly vaultTrack method working internally .
Hi I don’t see any challenge in your implementation.
In Corda we use Apache Artemis for RPC communication. The Corda-RPC library must be included on the client side in order to connect to the server.
Internally this works like this -
At startup Artemis will be created on the RPC client(client side) and RPC server (within the corda node), client and server queues are created, and sessions are enabled/established between client and server. The Corda-RPC library contains a client proxy, which translates RPC client calls to low-level Artemis messages and sends them to the server Artemis instance. These RPC requests are stored on the server side in Artemis queues. The server side consumer retrieves these messages, approprite RPC calls are made, and an acknowledgement is sent to the client. Once the method completes, a reply is sent back to the client. The reply is wrapped in an Artemis message and sent across by server Artemis to the client Artemis. The client then consumes the reply from client Artemis queue.
The client proxy within the the Corda-RPC library abstracts the above processes. From a client perspective you should only create the proxy instance and make the RPC calls.
I would urge you to use the Reconnecting Client. You can read more about this in a blog which I have written.
Also please read the last part in the blog which talks about how to handle reconnection/failover scenarios.
Related
I understand that gRPC is designed for client-server architecture. A server provides remote services and clients obtain the services by calling the defined RPCs. But is it possible for a client also defines a service so that other clients can request services from that client too?
An example, a server knows every client's locations and can inform other clients about the location information. A client, upon receiving the other clients' locations from the server, can now directly call the services provided by other clients.
Can gRPC do that? Thank you!
Yes, this is possible.
The terms "client" and "server" are overloaded in this context and would be better thought of as (stub) caller and (implementation) receiver. It's possible for the client and server to be the same process but then you don't need the complexity of gRPC.
There's no prohibition on some entity functioning as both a caller ("client") and receiver ("server"). This situation arises commonly, in peer-peer networks and in micro-services where some original client calls some service which (acts as a client and) then calls various other services ....
An endpoint connect to the Kaa server and subscribe some topics.
In normal condition, KaaClient's unsubscribeFromTopic() & stop() method will be called before disconnect the Kaa server.
In some cases, the endpoint maybe disconnect the Kaa server suddenly and won't re-connect to Kaa server immediately (ex: loss power...).
If an endpoint disconnect the Kaa server without call the unsubscribeFromTopic() & stop() method, the resource will still be occupied??
If yes, the Kaa server has heart-rate mechanism for all endpoints??
Will Kaa server kick off one endpoint automatically if it can detect the endpoint has disconnected exceed over a period time??
Short answer is yes, Kaa will free resources once no active connections are present. There is a ping-pong mechanism to track session inactivity. Inactivity timeout that will be used is configurable. See this configuration file for more details.
Extended answer: Kaa uses actor system based on Akka framework to handle endpoint requests/sessions. Each Endpoint has associated Endpoint Actor (actually, there are at least two of them, one on the node that handles endpoint session and one global actor for particular endpoint in the Kaa cluster). This actors schedule timeouts once no active sessions is available.
In the SignalR (server) hub I want do a license check. If the check negativ then I want in the OnConnected of the Hub block the connection. The client should get in the Hub start the Task as canceled with a message (no valid licence).
When I return a Task with a Aggregate Exception in the OnConnected of the SignalR Hub then the client gets a fault state, with a timeout exception.
How can I block the connection to the SignalR hub and give the client a message why I have block the connection?
As far as I know you can't just start or stop connections already on the server. The client has to disconnect itself. If you want to use the hub for licence check you need to have the client connect - send licence info - server checks and if it is invalid call $client.disconnect on the client.
The other option like blorkfish mentions is to allow them to connect, add them to a list and check this when they call methods on the server.
I don't think that you should block the connection with an Exception. Your client would then not be able to tell if there was a genuine error in the SignalR connection.
Rather send a specific SignalR message back that there is no license - and then manage the connection object on the server side.
Keep a list of licensed connections, and a list of unlicensed connections.
So instead of using Clients.All to broadcast, use Clients.Client("< client_connection_id >") to broadcast.
Hope this helps.
We have a requirement wherein the server needs to push the data to various clients. So we went ahead with SSE (Server-Sent events). I went through the documentation but am still not clear with the concept. I have following queries :
Scenario 1. Suppose there are 10 clients. So all the 10 clients will send the initial request to server. 10 connections are established. When the data enters the server, a message is pushed from server to client.
Query 1 : Will the server maintain the IP address of all the client? If yes is there an API to check it?
Query 2: What will happen if all the 10 client windows are closed? Will the server abort all connections after a period of time?
Query 3: What will happen if the Server is unable to send messages to client due to unavailability of client like machine shutdown. Will the server abort all connections after a period of time for those client for whom they are unable to send the message?
Please clarify?
This depends on how you implement the server.
If using PHP, as an Apache module, then each SSE connection creates a new PHP instance running in memory. Each "server" is only serving one client at a time. Q1: yes, but not your problem: you just echo messages to stdout. Q2/Q3: If the client closes the connection, for any reason, the PHP process will shutdown when it detects this.
If you are using a multi-threaded server, e.g. using http in node.js. Q1: the client IP is part of the socket abstraction, and you just send messages to the response object. Q2/Q3: as each client connection closes the socket, the request process that was handling it will end. Once all 10 have closed your server will still be running, but not sending data to any clients.
One key idea to realize with SSE is that each client is a dedicated socket. It is not a broadcast protocol, where you push out one message and all clients get exactly the same message. Instead, you have to send the data to each client, individually. But that also means you are free to send customized data to each client.
I connect to my server, which is load balanced for an alias to point to 2 servers, 01 & 02 and it round-robins connections for arguments sake. I can connect to the hub without a problem, and I can even send stuff to the server, but when it goes to return it to the client, I never get my methods invoked. If I bypass the load balancer and use the server name explicitly, it always works just fine.
I'm even tracing it, and I send back the message from the exact originating server with the Clients.Client(clientId).completeJob(stuff), and that executes fine on the server, but if I ContinueWith, it never gets finished.
Oh, and it's connected with server sent events. Am I missing something or is this just not supported?
Server-sent events establishes a long running connection, but unlike WebSockets, it isn't bidirectional. The connection can only be used to push data to the client.
SignalR uses regular XHRs to send data from clients when the WebSocket transport is unavailable. This means that the load balancer will likely route client-to-server hub method invocations to a server different than the one the client originally established a server-sent event connection with.
The server executing Clients.Client(clientId).completeJob(stuff) likely doesn't own the connection that would allow it to push a message to the specified client. (Though returning a value from a hub method on the server will send data back to the client via the same connection that invoked the method.)
SignalR can work behind a load balancer. It just requires a little more setup so all the SignalR servers can communicate with each other via a backplane such as Service Bus or Redis. This allows messages to get dispatched to the server that owns the server-to-client connection.
https://github.com/SignalR/SignalR/wiki/Azure-service-bus details how you can setup a Service Bus backplane on Azure.