I'm new to ArtemisMQ and absolutely don't understand the sense of connectors.
Why is connector essential, as we already specify accepter of Broker Server in broker.xml -> we know which port (it is accepter port) to send a request to if we want to connect to this server. Even if this server is part of cluster, what is a role of connector? There is also information from other part of documentation about "Clusters", but there is words about cluster connections :
The cluster is formed by each node declaring cluster connections to other nodes in the core configuration file broker.xml. When a node forms a cluster connection to another node, internally it creates a core bridge (as described in Core Bridges) connection between it and the other node, this is done transparently behind the scenes - you don't have to declare an explicit bridge for each node. These cluster connections allow messages to flow between the nodes of the cluster to balance load.
From documentation "Understanding Connectors":
connectors are used by a client to define how it connects to a server.
What does it mean "define how"?
I've already read and another question about connector, but it doesn't help me.
Additional questions:
Is connector always the same as acceptor(I've downloaded some official examples and all of them(that i've seen) have both same acceptor and connector )?
What information does connector encapsulates, if it only consists of host+port (and it is same as acceptor's (if we omit that acceptor host can me 0.0.0. or localhost))?
Why does stand-alone Broker have connector, for example by default creation ./artemis create?
What should we write in connector?
Can you give a simple example when acceptor and connector are
different?
Two important points to note:
A connector is not essential depending on your use-case. You'll find that the default broker.xml doesn't have any connector elements defined. For example, if you just run ./artemis create the generated broker.xml will not have any connector elements.
The documentation you cited is quite old (from the very first release of Artemis). You may benefit from reading the latest documentation which has been updated for clarity in many places.
As noted in both the documentation and the other Stack Overflow answer you cited, certain components in the broker need to connect to other brokers (e.g. core bridges, cluster-connections, etc.). A connector encapsulates the information necessary for these other components to make the connections they need. It's really as simple as that.
Now regarding your individual questions...
Even if this server is part of cluster, what is a role of connector?
In the case of a cluster using a broadcast-group and a discovery-group each node in the cluster needs to broadcast to all the other nodes in the cluster how the other nodes can connect to itself. It does this by broadcasting a connector which is referenced in the cluster-connection configuration. When the other nodes in the cluster receive this broadcast they take the connector information and use it to connect back to the node which broadcast it originally. In this way nodes can dynamically discover and connect to each other. It's also worth noting that in this case the connector configuration will essentially mirror one of the broker's acceptor configurations (since the connector will be used by other nodes to connect to the broadcasting node's acceptor). This is discussed further in the cluster documentation.
...connectors are used by a client to define how it connects to a server...
This bit of documentation you quoted is accurate but may be a bit confusing. Keep in mind that that a client can run anywhere, even within the broker itself. In the case of core bridges and cluster connections there is a client running in the broker which use the connector to determine how to connect to another broker. For what it's worth the updated documentation doesn't have this specific wording.
What does it mean "define how"?
A connector is the URL that the client needs to connect to the broker. The URL can simply include the host and port or it can contain lots of configuration details for the connection (e.g. SSL config).
Is connector always the same as acceptor..?
No, not always. In the case of a cluster they will be the same (or very close) for the reasons I already outlined, but in the case of a bridge they won't be the same.
What information does connector encapsulates..?
See above.
Why does stand-alone Broker have connector, for example by default creation ./artemis create?
It doesn't. See above.
What should we write in connector?
The URL needed to connect.
Can you give a simple example when acceptor and connector are different?
As mentioned previously, bridging is an example where different acceptors and connectors are used. ActiveMQ Artemis ships with a "core-bridge" example in the examples/features/standard directory which demonstrates different acceptors and connectors. The example involves 2 different brokers with one broker having a core bridge configured to send messages to the other broker. Here's the broker.xml with the bridge defined. You can see the acceptor listening on the localhost:61616 and the connector for localhost:61617. This connector points to the other broker which is listening on localhost:61617.
Related
We have setup a Kafka Cluster for High Availability and distributed data load. The current consumers and producers specify all the broker IP addresses to connect to the cluster. In the future, there will be the need to continuosly monitor the cluster and add a new broker based on collected metrics and overall system performance. In case a broker crashes, as soon as possible we have to add a new broker with a different IP.
In these scenarios, we have to change all client configurations, a time consuming and stressful operation.
I think we can setup a Config Server (e.g. Spring Cloud Config Server) to specify all the broker IP addresses in a centralized manner, so we have to change all in one place, without touching all the clients, but I don't know if it is the best approach. Obviously, the clients must be programmed to get broker list from config server.
There's a better approach?
Worth pointing out that the "bootstrap" process doesn't require giving every single broker address to the clients, really only the first available address in the list is used for the initial connection, then the advertised.listeners on all the broker configs in the cluster, is what the clients actually use
The answer to your question is to use service discovery, yes. That could be Spring Could Config, but the more general option would be Hashicorp Consul or other service that uses DNS (Kubernetes uses CoreDNS, by default, for example, or AWS Route53).
Then you edit the /etc/resolv.conf of each machine (assuming Linux) the client is running on to include the DNS servers, and you can simply refer to kafka.your.domain:9092 rather than using IP addresses
You could use a load balancer (with a friendly dns like kafka.domain.com), which points to all of your brokers. We do this in our environment. Your clients then connect to kafka.domain.com:9092.
As soon as you add new brokers, you only change the load balancer endpoints and not the client configuration.
Additionally please note that you only need to connect to one bootstrap broker and don't have to list all of them in the client configuration.
Is it compulsory to run kafka sink connector and ignite node on the same host?
If not, what changes I have to make in ignite configuration (XML) file to make it accessible from another node.
Thanks in advance.
Assuming the connector is a thin client, it doesn't need to be, however Connect shouldn't run on the brokers either, and if you're in a highly latent environment (consuming from the cloud / remote data center), then it's recommended that you "produce locally"
You'd change the Ignite server bind address (localAddress in the communications spi) to make it remotely accessible from any client, including other nodes in a cluster, assuming it isn't already
Has Kafka cluster and Kafka broker the same meaning?
I know cluster has multiple brokers (Is this wrong?).
But when I write code to produce messages, I find awkward option.
props.put("bootstrap.servers", "kafka001:9092, kafka002:9092, kafka003:9092");
Is this broker address or cluster address? If this is broker address, I think it is not good because we have to modify above address when brokers count changes.
(But it seems like broker address..)
Additionally, I saw in MSK in amazon, we can add broker to each AZ.
It means, we cannot have many broker. (Three or four at most?)
And they guided we should write this broker addresses to bootstrap.serveroption as a,` seperated list.
Why they don't guide us to use clusters address or ARN?
A Kafka cluster is a group of Kafka brokers.
When using the Producer API it is not required to mention all brokers within the cluster in the bootstrap.servers properties. The Producer configuration documentation on bootstrap.servers gives the full details:
A list of host/port pairs to use for establishing the initial connection to the Kafka cluster. The client will make use of all servers irrespective of which servers are specified here for bootstrapping—this list only impacts the initial hosts used to discover the full set of servers. This list should be in the form host1:port1,host2:port2,.... Since these servers are just used for the initial connection to discover the full cluster membership (which may change dynamically), this list need not contain the full set of servers (you may want more than one, though, in case a server is down).
All brokers within a cluster share meta information of other brokers in the same cluster. Therefore, it is sufficient to mention even only one broker in the bootstrap-servers properties. However, you should still mention more than one in case of the one broker being not available for whatever reason.
I have this question regarding configuring kafka listeners properties correctly -
listeners and advertised.listeners.
In my config I am setting below props:
listeners=SASL_PLAINTEXT://:9092
advertised.listeners=SASL_PLAINTEXT://u-kafkatst-kafkadev-5.sd.xxx.com:9092
The clients connect using u-kafkatst-kafkadev-5.sd.xxx.com:9092. Do I need to have the same value in listener and advertised.listeners. Here u-kafkatst-kafkadev-5.sd.xxx.com is a dns record that points to the host where kafka broker is running.
What are the situations where I would want to keep them same and different?
Thanks!
The advertised.listeners property is important if you are doing anything other than connecting to a broker directly on the same network. If you are using Docker, Kubernetes, IaaS (AWS, GCP, etc) then you need to expose the external address for the client to know where to connect to.
This article explains it all in depth.
I use to configure bootstrap.servers in my kafka producer/consumer/stream apps with a list of broker ips. But I’d like to move to a single url entry that will be resolved by the DNS lookup to a broker ip currently known as up (DNS actively check the brokers in the cluster and responds to lookup with an IP short TTL [10s]). This gives me more flexibility to add brokers in the future, and I can keep the same config in my apps across all the environments/stages. Is this a recommended approach, or this remove resiliency on the client side to not have a strict list of brokers? I assume this config would only be used to initially “discover” the cluster and the partition leader brokers.
If anything, I'd say this adds a single point of failure on the single address you're providing, unless it's actually a load balanced, reverse proxy.
Another possibility that's worked somewhat well internally is using Consul service discovery, with Consul agents running on each broker. This way, you can do service discovery as well as health checks and easier monitoring setup, e.g. having Prometheus jmx_exporter on the brokers, and Prometheus Server scraping those values for all kafka.service.consul addresses