Kafka - Publish once - Subscribe n times (by n components). If a publisher has to wait for its recipients to respond, then it will be limited in how much it can achieve at any given time. Kafka Topics are divided into partitions, and for each consumer group, the partitions are distributed among the various consumers in that group. RecordMetadata recMetadata = producer. sync=true but when the Kafka. To use App Connect to integrate Kafka with other connectors in the App Connect catalog, you need to connect App Connect to your Kafka environment. Synchronous Commands over Apache Kafka (Neil Buesing, Object Partners, Inc) Kafka Summit 2020 - Download as a PDF or view online for free. There are two common ways Microservices communicate with each other: Synchronous and Asynchronous. The topic name is build based on the process_id of the python Application (Flask/uwsgi). Thus, if API client and API implementation are not both available throughout the duration of the API invocation then it fails. In most cases the correlation id will be a natural id of the entity. In this context, a “request” consists of publishing a message to the. One of our usecase is to receive a message from an api produce it to topic1 and and the result to. User Authentication Service which returns the auth token as the response and until we. send (new ProducerRecord<String, String> ("topic-name", "key", "value")). com Kafka Request- Async Reply Pattern. This talk discusses multiple options on how to do a request-response over Kafka — showcasing producers and. Pub-sub is a way to decouple the two ends of a connection and communicate asynchronously. Hence it should be used only when needed. Enterprise messaging technologies, such as IBM MQ, RabbitMQ and ActiveMQ, have provided asynchronous communication within and across applications for many years. An entity topic is one of the most helpful ways to use Kafka to. Stack Overflow | The World’s Largest Online Community for DevelopersProcess streams of records in real-time. Netflix operates at a scale of approximately 1 million events per second. 2. When you aim for a request/response pattern, you typically want a synchronous response, like if the user sends a command to the. The user is waiting for data until this response is. If it is 0 the server will not send any response. Connect and share knowledge within a single location that is structured and easy to search. e. gRPC-Kafka Proxying. If combining Event Notification using Kafka with traditional Request-Response, it may be. Provide broker log excerpts. AttributeMap But while it sort of works sometimes one request overwrites the details of another request. but I am not yet clear why it is not. The consumer has significant control over this position and can rewind it to re-consume. Kafka is a powerful stream processing tool, but it's an asynchronous tool. Recently, event streaming technologies (such as Apache Kafka) have grown in popularity, and they also provide asynchronous communication. But I have to send the response back the result as response back to API gateway and back to front-end application. (by modifying the ProductAddedNotification to publish to Kafka/Service Bus,. a high-speed message queue like Kafka or ActiveMQ Artemis, or as a direct call. $ mkdir npm-slack-notifier && cd npm-slack-notifier. Make synchronous request. So we used ReplyingKafkaTemplate So that we can instantly respond back to Caller. As shown in Figure 1, for each request (REST, GraphQL, gRPC), a response follows. Synchronous behaviour: Client constructs an HTTP structure, sends over the socket connection. Kafka client generates a random UUID and sends a single Kafka request message. I understand that the Callback can return a series of retriable and non-retriable exceptions. I would like to have a global exception handler for the RestTemplate where I can catch all the exceptions, and then return a response to the original sender of the event. camel-aws-kinesis-kafka-connector sink configuration. OkHttp supports Android 5. Therefore, additional information and insights on the actual needs and requirements were needed to. Part 6: Leveraging the Power of a Database Unbundled. I want to use request topic and corresponding requestreply topic dynamically generated on the basis of request sent from user (UI). Looking around it seems that using the inbound channels AttributeMap could be the place to store such request details. Request Response. Open the file server. A community-developed, free, opensource, automated testing framework for microservices API, Kafka and Load testing. Unfortunately, the battle is an apple-to-orange comparison that often includes misinformation and FUD from vendors. An asynchronous client constructs an HTTP structure, sends a request, and moves on. Example of such communication is REST (Representational State Transfer) based APIs where request and response are sent through HTTP (Hyper TextWhen connecting, the client will request the server to send response messages through setting the request-response information attribute in the CONNECT packet. Synchronous Request Response Model ; Asynchronous Publish Subscribe Model ; What are Message Queues ; Different Message Queues: ; RabbitMQ ; Kafka ; ActiveMQ ; IBM MQ Synchronous Request Response Model The client makes a request to the API and has to wait for the response until all the processing has. 3, last published: 5 years ago. Asynchronous APIs return calls instantly. requests. 1. Producers and consumers of messages are decoupled by an intermediate messaging layer known as a message broker. However, CQRS and event sourcing is the best and more natural solution for data streaming. New search experience powered by AI. 0. hystrix. Thus, service A sends a request for data to B in REST and waits for the response of this request in Kafka. I'm trying to research the way to apply Kafka in the legacy system which has an oracle form was written in PL/SQL function. As far as I understand, the problem is that we do not use the built-in Kafka ACL mechanism for restricting access to Kafka-topics, but we use the Rager-Kafka-Plugin. The question is, would the benefits be worth the effort in your particular circumstances. There are various techniques, each with advantages and disadvantages. Figure 2-1. But I have to send the response back the result as response back to API gateway and back to front-end application. Can anyone please guide me how can I achieve the synchronous request and response between API gateway and micron service via Kafka. Synchronous APIs often use HTTP or HTTPS for transport, and HTTP is a unidirectional protocol. Finally, we can put all these ideas together in a more comprehensive ecosystem that validates and processes orders in response to an HTTP request, mapping the synchronous world of a standard REST interface to the asynchronous world of events, and back again. Set a function to be called to establish a unique correlation key for each request record. id that uniquely identifies this Producer client. Apache Kafka version. At a high level, they all support some form of messages. 12 min read. However, you can achieve request-response using asynchronous messaging. In this post, we will create an OkHttp GET HTTP request example in Java. Kafka is a powerful stream processing tool, but it's an asynchronous tool. The consumer remains as it is. Connect and share knowledge within a single location that is structured and easy to search. It works for you because the send method returns void, so Spring executes its content inside a new thread and returns immediately to send's caller. The user sends an HTTP request to the UI Service (there are multiple UI Services) that fires some events to a queue (Kafka/RabbitMQ/any). JS. In conventional synchronous mode of communication, we have the request-response type of communication where one service sends a request to another service, which replies by sending the response. 2. For a part of this application (Login and Authentication), I need to implement a request-reply messaging system. You can increase the timeout (the default is 5 seconds) but you should look on the server side to see why the reply is not being sent, if you expect. I'm working on a micro service powered by SpringMVC and Spring Cloud Kafka. In this case, you use Kafka to pass notifications of what happens in the different services. The controller subscribes to this response topic to receive the response to the query initiated. I have an endpoint which pushes data to kafka. Once the message is received. With some effort you can do async with REST and sync with MQ. This way, you would be able to catch any exception thrown by the blocking invocation and act accordingly. So we know when we send the request but we don't know when the answer will come. Kafka is a high-performance, low-latency, scalable and durable log that is used by thousands of companies worldwide and is battle-tested at scale. You have built an event-driven system leveraging Apache Kafka. A CompletionStage is an interface that models a stage of a possibly asynchronous computation, that performs an action or computes a value when another CompletionStage completes. 1M seed round led by 468 Capital with participation from Pear VC, Alumni Ventures and an angel syndicate including former NGINX CEO Gus Robertson and DigitalOcean. . Oct 27, 2022. Request and response topics are more or less what they sound like: A client sends a request message through a topic to a consumer; The consumer performs some action, then returns a response message through a topic back to the consumer. This is simple to implement, but if the requestor crashes, it will have difficulty re-establishing. Creating the project. "Kafka Streams, Apache Kafka’s stream processing library, allows developers to build sophisticated stateful stream processing applications which you can deploy in an environment of your choice. First, we need to invoke a Kafka producer a message as a rest service, they will process and give back the response in another topic. If combining Event Notification using Kafka with traditional Request-Response, it may be necessary to implement synchronous semantics on top of asynchronous Kafka topics. When the function completes, Lambda returns the response from the function's code with additional data, such as the version of the function that was invoked. blog-synchronous-kafka. Message processing is synchronous. Synchronous Send. For delayed responses, you need to implement asynchronous communication based on. We also saw the basics of producers, consumers, and topics. timeoutInMilliseconds. Apache Kafka is a an open-source event streaming platform that supports workloads such as data pipelines and streaming analytics. This separation is often achieved by use of the Queue-Based Load Leveling pattern. 12-2. Therefore, we need the ability in KafkaUI to disable the functionality for Kafka ACL discovery from the Kafka server. Learn more about TeamsAnother approach for decoupling synchronous HTTP messages is a Request-Reply Pattern, which uses queuing communication. In nest js, Kafka transporter supports both request-asynchronous response style messaging out of the box. It's as asynchronous as it can be. To create a Kafka producer, you will need to pass it a list of bootstrap servers (a list of Kafka brokers). Asynchronous tasks are tasks that can be processed in the background and are not time-sensitive. It will allow the logging, metrics, and tracing to be linked together for a particular request in the centralized. New search experience powered by AI. Apache, Apache Kafka. ·. Sorted by: 66. One of EIP is Request-Reply. g. For example, for the create_user message type, the response can be user_created and will include the user_id, so this is enough. " as necessary in configuration). But still the receiver of the response throws No pending reply exception. Oct 27, 2022. At the same time, it holds the request awaiting until the response returns or a timeout occurs. The Kafka consumer works by issuing “fetch” requests to the brokers leading the partitions it wants to consume. It simply means the request was sent, but the reply wasn't received in time; it's hard to see how adding debug logging on the client side will help; the template is simply waiting for thee reply. Record latency t 1 – t 0. The biggest limitation of the REST Proxy data plane is that it is a synchronous request-response protocol. In this article, we will write a code using Java 1. Apache Kafka or any messaging system is typically used for asynchronous processing wherein client sends a message to Kafka that is processed by background consumers. In the synchronous case you have to choose how many servers need to acknowledge the message before your thread can continue. And in some cases, there are some synchronous applications which fronts Kafka. Comparing JMS-based message queue (MQ) infrastructures and Apache Kafka-based data streaming is a widespread topic. Deal over. Synchronicity: API invocations are by definition synchronous, consisting of request and synchronous response, even though the processing triggered by an API invocation can be performed asynchronously. Nest automatically sends the reply back in a new event that ends with a . Enterprise messaging technologies, such as IBM MQ, RabbitMQ and ActiveMQ, have provided asynchronous communication within and across applications for many years. If the response is not received. Can I use Pact V4 Synchronous Messages to write contract tests for Kafka with request-response pattern? #1681. I am doing a search on something and there is a delay in getting the results. 8+. So the API response might not have the expected string until after waiting for a few seconds. I am using the same replyTopic and correlationId as received in the consumer to publish the event. When the function completes, Lambda returns the response from the function's code with additional data, such as the version of the function that was invoked. HTTP/REST and Kafka are frequently combined to take advantage of the best of both worlds: decoupling with Kafka and synchronous client-server communication with. Microservice 1 - is a REST microservice which receives data from a /POST call to it. How to achieve this? apache-spark. Synchronous messaging is possible but impacts scalability. NET Core websites via RabbitMQ queues using MassTransit . Technically, these are two. With synchronous messaging, the Requestor makes a request and the transport layer code blocks waiting. Part 4: Chain Services with Exactly Once Guarantees (Read Next) Part 5: Messaging as the Single Source of Truth. command. light-tram-4j and light-saga-4j and replaced them with light-kafka for Event Sourcing and CQRS framework. HTTP is a Request/Response Protocol. But I have to send the response back the result as response back to API gateway and back to front-end application. You should always use service tasks for synchronous request/response. See the documentation. Hình bên dưới là là 1 service minh họa đơn giản để tính tổng của 2 số yêu cầu đồng bộ (synchronous – sử dụng mô hình Request-Reply). Hide the complicity of Kafka client. Typically synchronous Point to point Pre-defined API Event streaming (Kafka) Continuous processing Often asynchronous Event-driven General-purpose events Most architectures need request-response for. Kafka nuget version. You have built an event-driven system leveraging Apache Kafka. Communication is synchronous when one service sends a request to another service and waits for the response before proceeding further. Reading data from Kafka is a bit different than reading data from other messaging systems, and there are few unique concepts and ideas involved. Now, we want to take the same example and change the send () method call to a synchronous blocking call. Set to false to use the String representation of the correlation as the correlationId rather than the binary representation. Request Response in Spring. Configure each website to use MassTransit to communicate via a local RabbitMQ queue. Nest js provides an option to listen to the response topic from the Kafka broker. Event sourcing and Apache Kafka are related. They are generally associated with user actions that need immediate system response. Here’s how – Event sourcing involves maintaining an immutable sequence of events that multiple applications can subscribe to. connection = 1, it just means the ordering of messages is guaranteed within a partition it has nothing to do with synchronization. Request and response topics: Async API. Zerocode Open Source enables you to create, change, orchestrate and maintain your automated test scenarios declaratively with absolute ease, without writing code - Producing and consuming XML message to and from a. This talk discusses multiple options on how to do a request-response over Kafka — showcasing producers and consumers using single and multiple topics, and more. Apache Kafka is by design inherently asynchronous. Synchronous requests are sequential, leading to delays; asynchronous enables parallel processing. Event Driven Architectures using Apache Kafka are gaining lots of attention lately. When Service A makes a blocking synchronous call to Service B, it must wait to get the response (or acknowledgment) that the request is completed. The enriched message is. 6. The Grpc implementation will fail immediately after disconnecting the consumer, and grpc must be configured. A Kafka producer has three mandatory properties: 1. 4). The producer is thread safe and sharing a single producer instance across threads will generally be faster than having multiple instances. request. Exposing and calling an endpoint (often called WebAPI in . Get the latest news from us to your. The problem with a lot of benchmarks is that they end up measuring service time rather than response time,. Asynchronous Request-Response with Apache Kafka. A synchronous request is considered blocking: the response is needed for the process to continue. The issue is that multiple services can trigger user_create workflows, and they will expect for the response. Quarkus provides support for Apache Kafka through SmallRye Reactive Messaging framework. When you invoke a function synchronously, Lambda runs the function and waits for a response. The market is changing, though. Hình bên dưới là là 1 service minh họa đơn giản để tính tổng của 2 số yêu cầu đồng bộ (synchronous – sử dụng mô hình Request-Reply). kafka. Apache Kafka 0. 8. 0. Q&A for work. we can run it), minimal program demonstrating the problem. Synchronous Commands over Apache Kafka. JS client --> Spring RestController --> send request to Kafka topic --> read response from Kafka reply topic --> return data to client. Check out “ Service Mesh and Cloud-Native Microservices with Apache Kafka, Kubernetes and Envoy, Istio, Linkerd ” for more details on this topic. Asynchronous Messaging over HTTP. When using a synchronous, request/response‑based IPC mechanism, a client sends a request to a service. Asynchronous — Message Queues, Databases, Files, E-Mail, Cloud storage One of EIP is Request-Reply. g. to stop zookeeper and kafka (later) docker-compose rm -fsv. springframework. 4. Provide logs (with "debug" : ". When you specify a service in the "Resource" string of your task state, and you only provide the resource, Step Functions will wait for an HTTP response and then progress to the next. I'd like to route a webservice request to an InOnly endpoint of a jms queue. Asynchronous tasks (fire-and-forget, or making use of a call-back mechanism) are. Most developers are familiar with blocking synchronous calls. id. As far as I understand, the problem is that we do not use the built-in Kafka ACL mechanism for restricting access to Kafka-topics, but we use the Rager-Kafka-Plugin. Developers and architects might incorrectly. Event-driven architecture enhances real-time experience and efficiency. I can able to achieve the sync by using spring. Asynchronous processing is the opposite of synchronous processing, as the client does not have to wait for a response after a request is made, and can continue other forms of processing. a message queue-based implementation has some advantages. The code snippet is. consumer. Kafka is a high-performance, low-latency, scalable and durable log that is used by thousands of companies worldwide and is battle-tested at scale. Synchronous — HTTP, Sockets 2. See the documentation. We can use the non-blocking call if application requirements permit. Each partition is an ordered, immutable. Request-Reply is a common pattern in modern distributed systems. The property visible below sets the time after which the caller will receive a timeout while waiting for a response: 1. So I try to use ReplyingKafkaTemplate. It has nothing to do with REST webservice, its structure, or the supporting server. I am developing a series of microservices using Spring Boot and Kafka. I have a use case where I require synchronous communication between two microservices (a user registers a profile via the user profile service which needs to create an auth account in the auth. Send task Technically, send tasks behave exactly like service tasks. i. Each consumer is responsible for consuming the messages in the partitions is gets assigned. Publish/asynchronous response - a service publishes a request to one or recipients, some of whom send back a reply; Examples. Apache Kafka or any messaging system is typically used for asynchronous processing wherein client sends a message to Kafka that is processed by background consumers. My understanding of your code fragments is that you made your own code asynchronous by using the spring way to do it. Net) is a much simpler solution. Kafka, on the other. Kafka client generates a random UUID and sends a single Kafka request message. Waits for the response HTTP. One of EIP is Request-Reply. Recently, I found an easier approach to deal with the request-reply pattern. The second is asynchronous, and the returned Uni gets the response when received. Share. Service A receives a request from a consumer for data that is stored in service B. With some workaround, we can make this communication synchronous (request-response pattern). Not quite. The monolithic way of doing thing is that I've a User/HTTP request and that actions some commands that have a direct synchronous response. @inf3rno All I was trying to say was that with REST it is much easier to use synchronous request-response style, whereas with messaging asynchronous is easier and more natural. The framework then echoes the correlation id into the reply and uses the topic for the destination. It relies on asynchronous message-passing instead of synchronous request response-based architecture. That's why in Kafka, the number of partition in. So I keep executing the POST request until the response has the. Waits for the response HTTP. See KafkaConsumer API documentation for more details. After I explained that request-response should not be the first idea when building a new Kafka application, it does not mean it is not possible. send (“ngdev-topic”, key, value). However, the alternative symbol makes the meaning of sending a message easier to. In this case, the caller thread is not blocked and can do something else. Kafka Connect REST APIs finds various use cases for producing and consuming messages to/from Kafka, such as in: Natural Request-Response Applications. However, I came across a requirement of implementing request/response paradigm on top of Apache Kafka to use same platform to support both sync and async. Applications that need to read data from Kafka use a KafkaConsumer to subscribe to Kafka topics and receive messages from these topics. Event-driven architecture enhances real-time experience and efficiency. The general idea is that the publisher includes a destination for a consumer to publish another message with the reply/response. You’ll create a simple Gin web API where a user can send a notification to another user via an HTTP POST request. In this post I describe how I was able to handle a synchronous request/response with kafka. Tiny Java library to provide synchronous request-response behaviour on top of Kafka for applications that must publish a Kafka "request" message and then await a Kafka "response" message. The consumer receives back a chunk of log beginning from the offset position. This plugin uses Kafka Client 3. So we know when we send the request but we don't know when the answer will come. Apache Kafka version. Examples: WebSocket , MQTT , Server-side Events (SSE), or the Kafka protocol (the. With the latest release of spring-kakfa, we are trying to use request-reply semantics and would like to know if we can use intermediate topics with out losing correlation id. The Asynchronous Request-Response conversation involves the following participants: The Requestor initiates the conversation by sending a Request message amd waits for a Response message. In Quarkus with smallrye reactive messaging the code would look something like below wrapping the payload with. These microservices answer to the Gateway (then to the client) on a topic set in the request object. Rather I am getting warning in the code for unsuccessful send (as. This pattern is a little less generally useful than the previous two. default. Then responsible service prepares an Response and provides. Request goes to load balancer, and then forwarded to a web server that is part of an auto scaling group of web servers. I know this can be achieved by using simple REST calls. Kafka (0. In this case, all instances receive each reply, but only the instance that sent the request finds the correlation ID. So I have the restriction to implement the batch request in synchronous mode as it deliver individual DR per message, because it is very important to deliver the response for the batch request. Synchronous Send. Viewed 101 times. A synchronous wrapper is a stateful component. The software is composed of independent small services in microservice architecture that communicate over well-defined APIs. , May 25, 2022 (GLOBE NEWSWIRE) -- Aklivity, the company pioneering streaming API management, today announced an oversubscribed $4. Recently, event streaming technologies (such as Apache Kafka) have grown in popularity, and they also provide asynchronous communication. But if we want to use request-reply pattern we can use communication, even though we can use Kafka in request-reply pattern with some workaround. There are various techniques, each with advantages and disadvantages. Synchronous — HTTP, Sockets 2. In a typical request/response synchronous messaging scenario, you will find a service (server) and a consumer (client) that invokes the service. Synchronous communication requires synchronous mediums and Kafka is not one. Kafka Synchronous Producer Example code. So today we will see the first of 3 cases to make this communication between the synchronous. $ npm install --save kafkajs npm-hook-receiver @slack/webhook. <parent>. In the async case, the kafka producer library will put your request in an internal queue, and unless that queue is full, you’ll get control back to your main thread immediately. thread. Check if your favourite Kafka proxy or cloud API supports the HTTP streaming mode. e. When one service needs in some data it sends a Request to the other service which is responsible of such data. g. In a PULL paradigm the client has to initiate a request and poll the server for receiving new data, which is half-duplex and unidirectional . Stack Overflow | The World’s Largest Online Community for DevelopersThe app that is handling the sync API (such as a REST API call over HTTP) would publish to a request topic, including in the request message a unique CorrelationID (that you generate in your app) and then at the other end, your Async app can processes these requests from the request topic, and reply to a response topic using the. I am able to get request-reply response from synchronous kafka. 9 client for Node. Here’s the key things to know about asynchronous APIs: Synchronous APIs provide instant responses; asynchronous APIs use callbacks. Teams. Apache Kafka and Publish/Subscribe messaging in general seeks to de-couple producers and consumers through the use of streaming async events. Intermediate Topics in Synchronous Kafka: Using Spring Request-Reply. Sorted by: 66. */ public static final String PREFIX = "kafka_";. Bridging the Synchronous and Asynchronous Worlds. The request data received at API Gateway is forward to Micro service via Kafka. When the server receives a connection, it uses that thread to read the request, process it, and write the response. When one service needs in some data it sends a Request to the other service which is responsible of such data. to stop zookeeper and kafka (later) docker-compose rm -fsv. The property visible below sets the time after which the caller will receive a timeout while waiting for a response: 1. The biggest limitation of the REST Proxy data plane is that it is a synchronous request-response protocol. Part 3: Using Apache Kafka as a Scalable, Event-Driven Backbone for Service Architectures. kafka. The original thread, or another thread, can then process the response. acks=1 – When we set the Kafka ack value to 1, the producer receives an acknowledgment as soon as the leader replica has received the message. cd spring-kafka-server mvn spring-boot:run. The subscribers then consume events from the publishers. Synchronous tasks are high-priority tasks that require immediate execution and user feedback. (currently we are using AQ(Oracle AQ) in the system, but now I have to change to Kafka) Example :This endpoint returns 202 Accepted with a link to check on the task status. We are having several microservices in our product, there are some business use cases where one microservice (TryServiceOne) have to delegate request to another microserice (TryServiceThree). get () -> . This process is often referred to as blocking (i. Author: Syarif Hidayat - Analyst. 0. Send messages to a particular topic with the payload and event key ID. In this example, we are going to send messages with ids. To invoke a function synchronously with the AWS CLI, use the invoke. This is where the combination of MuleSoft and Apache Kafka shines. In a distributed system, this can increase the latency of an application since the service may be hosted in another process, on another machine, or may even be a remote service in. Thus, to respond to the same User/HTTP request is 'hassle free'. Kafka, for subscribed consumers to then receive and act upon. Request–response; Request. a message queue-based implementation has some advantages. A Kafka Example for the Request-response Pattern. 4. Hans. The Provider waits for incoming Request messages and replies with Response messages. The most used architecture to ensure this is the microservice architecture. Class này kế thừa các tính chất của KafkaTemplate để cung cấp mô hình Request-Reply. Request and response topics are more or less what they sound like: A client sends a request message through a topic to a consumer; The consumer performs some action, then returns a response message through a topic back to the consumer. There are four Kafka topics involved: a request and a response topic for the credit approval messages, and a request and a response topic for the payment messages. Request Response (Synchronous) Pattern. if the consumer is down, the request will be received when the consumer is active and will respond to the producer with some delay. REST is purely an HTTP transport based call and you will receive a response say 200 OK on the other side, SOAP uses two varieties, Synchronous Messaging over HTTP. Database, JMS, MQ, Kafka, and others: 10 MB. Steps to reproduce. However, the spring-kafka calls you make remain synchronous. 3. This application is written entirely using Python. Synchronous communication is the most straightforward solution when trying to make services communicate. I am going to use Kafka as a message broker in my application. 2. HTTP 1. e. In this blog post, I’ll review the Kafka ecosystem and tools and discuss the different options for MuleSoft and Kafka collaboration. Services can use synchronous request/response‑based communication mechanisms such as HTTP‑based REST or Thrift. The user is waiting for data until this response is received.