I brought up Hermes using “vagrant up” and it successfully came up . Got the below links to access the components too.
UI & Management: http://10.10.10.10:8090
Frontend: http://10.10.10.10:8080
Graphite: http://10.10.10.10:8082
But when I actually paste the links in a browser , it says page isn’t working . Has something changed from the documentation ?
@tnagy81 Hi,
When we started implementing Hermes six years ago, spring-boot wasn’t so popular then. Hermes-management at the beginning was written in Jersey framework which in internals uses hk2 as a light-weight dependency injection framework. So we started with hk2 in hermes-management and decided to use it in hermes-{frontend, consumers} as well.
When spring-boot gained popularity we’ve rewritten hermes-management to use it. However we didn’t use spring-boot in hermes-{frontend, consumers} due to performance reasons.
Hermes-frontend has to be very fast. Therefore we’ve written it on a raw HTTP handlers in Undertow server. spring-boot-starter-web adds additional layers such as servlets implementation and custom filters. They add additional latency for request processing and we don’t want that.
So, as you see there are two reasons, historical and performance, why we don’t use sprint-boot in hermes-{frontend, consumers}. Today, replace of hk2 to spring di framework in hermes-{frontend, consumers} is not a trivial task as it requires rewrite of a lot of code. However, it would be nice to have the same dependency injection framework and configuration method in all Hermes modules. We don’t do this task in our team as we have other priorities right now but in the future it would be nice to do it.
schema.repository.url: URL of repository Also what about this URL of repository? Which URL is expected?
@shimnarkrishnan_twitter
"Also what about this URL of repository? Which URL is expected?"
Both schema repo and schema registry provides http API to manage schemas so you have to provide the server URL where your repository is running.
This URL must have the following form: http://<host>:<port>. By default it is http://localhost:8888/."I couldn't figure out where to set the below configurations schema.repository.type: schema_registry"
You have to add these properties to your configuration files. You can look at my development hermes configuration (based on docker containers) where I have configured schema-registry: https://github.com/jewertow/hermes-dev-environment.
Schema-registry configurations:
- hermes-management: https://github.com/jewertow/hermes-dev-environment/blob/master/modules/management/management.yaml#L58
- hermes-consumers: https://github.com/jewertow/hermes-dev-environment/blob/master/modules/consumers/consumers.properties#L14
- hermes-frontend: https://github.com/jewertow/hermes-dev-environment/blob/master/modules/frontend/frontend.properties#L13
Schema-registry container configuration: https://github.com/jewertow/hermes-dev-environment/blob/master/docker-compose.yml#L31
@shimnarkrishnan_twitter
Ad 1) Yes, it does. By default message size is a soft limit, warn log is emitted when message larger than declared topic message size is received.frontend.force.topic.max.message.size flag can be switched to make it a hard limit (Frontend will return
http 413 Payload Too Large status).
Ad 2) Schemas are kept in schema-registry. Zookeeper in Hermes is used as metastore to keep information about topics and subscriptions such as topic name, description, owner, max message size, attached subscriptions, subscription name, endpoint, retry policy, etc.
Ad 3) Didn’t use it but I see it supports HTTP & JSON so at first glance it should be possible to use it on Hermes
@PostMapping
public String testConsume() {
System.out.println("hi");
return "hello consume";
}
@shimnarkrishnan_twitter
Could you describe how did you create the subscription for this endpoint?
Did you create it according to the documentation (https://hermes-pubsub.readthedocs.io/en/latest/user/subscribing/#creating-subscription) ?
You can also check out example in my development environment:
- How subscribing service should work: https://github.com/jewertow/hermes-dev-environment/blob/master/modules/subscriber/src/main/java/com/github/jewertow/App.kt#L28 - it is simple Ktor app, but you can replace it with spring boot
- How to create subscription in Hermes: https://github.com/jewertow/hermes-dev-environment/blob/master/setup-data.sh
There is a README file, you can follow the instructions and easy setup working environment.
@tnagy81 I'm glad I could help
@shimnarkrishnan_twitter
- set message ttl on your subscription to a low value such as 10 seconds
- publish a message on the topic
- after 10 second refresh the subscription in a browser and verify what you see in “Last undelivered message” panel. You should see the reason why message wasn’t delivered.
if you want to track every message by hermes message tracking mechanism you have to install trace storage: https://hermes-pubsub.readthedocs.io/en/latest/configuration/message-tracking/
hermes-management module and ran into an issue because some spring auto configuration. This sounds spring related but actually the cause of it is that spring-mvc is present on the classpath and two frameworks are listening to requests. I have found spring-boot-starter-web in the dependencies of hermes-management. If you are using spring-boot-starter-jersey it is unnecessary to add starter-web because it will hook up spring MVC which you don't need for JAX-RS endpoints. My workaround was adding spring-webmwc to exclusions (I am using maven) of hermes-management dependency. My service and of course the hermes components start without any issue and endpoints are working fine. Though I did not check all the endpoints :DI wanted to make a hermes build without the spring-boot-starter-web dependency to check whether it will be successful with all the test but I did not have time to do it yet.
spring-webmvc stuff just only because of vacations. I'd really like to contribute though. As far as I understand if we handle this as a small issue I don't have to create a ticket. I also want to note that if I remove spring-webmvc then Spring Actuator endpoints (like /health, /info) start to work in hermes-management which is nice to have.
1 reply
@shimnarkrishnan_twitter few years ago we had occasionally problems with docker on different laptops. On one laptops it worked, on others it didn’t, especially after docker updates. Therefore we decided to use Vagrant in our quickstart guide. However, I see that docker is much more stable technology now and our open source users are asking about it, so we are planning to bring it back in Hermes. In the near future we are going to publish new images of Hermes on dockerhub :)
As for Kafka and Hermes. Hermes for Kafka is a client. If you already have a running Kafka cluster on production and you are happy with it then run of Hermes on it should be easy and smooth :)
Hi @bensonmiller, you are the first user who would like to use Hermes with Kafka from Confluent Cloud. So far, we didn’t have that need, but definitely Hermes should be compatible with Confluent Cloud as well. Although, keep in mind that Hermes will still need a Zookeeper cluster to run.
As you noticed, Hermes uses Kafka zookeeper client to manage topics configuration. I will create an issue to replace this old client to something new. When we resolve it, then will see whether something more has to be done to be compatible with Confluent Cloud. Please let me know if this approach is ok for you :)
We have a very special case. Hermes will post messages on topic, but one (old) service will have to read from Kafka directly (akka cluster + sharding).
thx
Last time you heard form me I was stating that spring-webmvc is not a necessary dependency for hermes-manager. I went a bit deeper in this topic and unfortunately (or fortunately) I was wrong. It is needed for the static content of the console. I admit that I don't have any experience with jersey and I thought that jersey starter is enough.
Anyway, I have a few other questions:
- Is it allowed in case of
httpsto define a subscription URL with non standard port? - I'd like to develop a service that sends an automated notification (e.g.: email) in case a subscription is unhealthy. Can you give some basic ideas how to do that, what would be the best practice to regularly check subscriptions health?
- Retries and offset: As far as I understand from the code the kafka offset is committed in a separate thread. Also message processing does not stop when a previous message is in the retry loop. I'd like to understand what happens if there are too many retries and what happens if one hermes-consumer instance fails/shuts down/is killed not gracefully? What are the chances of messages being resent multiple times, losing messages, resending huge amount of already sent messages.
- What happens to the offset commit when there is one or more message that is being retried?
- I assume that retries stay in the message sending queue. Does that mean that if the queue is filled with retries than reading of the topic will stop until retries succeed or expire?
- Is there any automated suspend?