Is there a way to check whether zookeeper connection is lost while running Spring boot application ? After some research I came across health indicators from spring boot . But i cant find any article related to checking the health of the zookeeper connection from Spring boot. Or is there a simple,effective way out without using Health indicators ?
springboot has spring-cloud-zookeeper, it has ZookeeperHealthIndicator . if you use spring-cloud-zookeeper you do not need to care about it. or you can write your own zookeeper health indicator and take it as a reference.
Related
When using the Lettuce to connect redis cluster, if a slave node is unavailable, springboot health check will fails, but actually the read and write of the application are normal. Is this the design or a bug?
springboot: 2.3.12.RELEASE
I have two docker instances that I launch with docker-compose.
One holds a Cassandra instance
One holds a Spring Boot application that tries to connect to that application.
However, the Spring Boot application will always fail, because it's trying to connect to a Cassandra instance that is not ready yet to take connections.
I have tried:
Using restart:always in Docker-compose
This still doesn't always work, because the Cassandra might be up 'enough' to no longer crash the Spring Boot application, but not up 'enough' to have successfully created the Table/Column family. On top of that, this is a very hacky solution.
Using healthcheck
It seems like healthcheck in compose doesn't have restart capabilities
Using a bash script as entrypoint
In the hope that I could use netstat,ping,... whatever to determine that readiness state of Cassandra
Right now the only thing that really works is using that same bash script and sleep the process for x seconds, then start the jar. This is even more hacky...
Does anyone have an idea on how to solve this?
Thanks!
Does the spring boot service defined in the docker-compose.yml depends_on the cassandara service? If yes then the service is started only if the cassandra service is ready.
https://docs.docker.com/compose/compose-file/#depends_on
Take a look at this github repository, to find a healthcheck for the cassandra service.
https://github.com/docker-library/healthcheck
CONCLUSION
After some discussion we found out that docker-compose seems not to provide a functionality for waiting until services are up and healthy, such as Kubernetes and Openshift provide (See comments below). They recommend to use wrapper script (docker-entrypoint.sh) which waits for the depending service to come up, which make binaries necessary, the actual service shouldn't use such as the cassandra client binary. Additionally the service depending on cassandra could never get up if cassandra doesn't, which shouldn't happen.
A main thing with microservices is that they have to be resilient for failures and are not supposed to die or not to come up if a depending service is currently not available or unexpectedly disappears. Therefore the microservice should be implemented in a way so that it retries to get connection after startup or an unexpected disappearance. Unexpected is a word actually wrongly used in this context, because you should always expect such issues in a distributed environment, and even with docker-compose you will face issues like that as discussed in this topic.
The following link points to a tutorial which helped to integrate cassandra properly into a spring boot application. It provides a way to implement the retrieval of a cassandra connection with a retry behavior, therefore the service is resilient to a non existing cassandra database and will not fail to start anymore. Hope this helps others as well.
https://dzone.com/articles/containerising-a-spring-data-cassandra-application
I have Spring boot mongo db app, when i start running this application if mongo host is alive, am able to see the my app is up and running successfully,
if my mongo host is down when i start my application my app failed to start.
is there any way even thought if mongo host is down my application should be up and running.
could someone please help me on this?
am using spring boot mongo properties in my application
spring.data.mongodb.repositories.enabled=true
spring.data.mongodb.port=27017
spring.data.mongodb.database=db
spring.data.mongodb.uri=mongodb://mongo-node-1.ballu/db
have same problem with spring boot kafka also.
Sorry for the previous comment. It was for excluding auto config beans, anyway
Is there any way even though if mongo host is down my application
should be up and running.
Yes,
spring.datasource.continue-on-error=true #Whether to stop if an error occurs while initializing the database.
as per spring doc
By default, Spring Boot enables the fail-fast feature of the Spring
JDBC initializer. This means that, if the scripts cause exceptions,
the application fails to start. You can tune that behavior by setting
spring.datasource.continue-on-error.
and as of spring kafka try this(i'm not sure if this meets your requirement)
spring.kafka.admin.fail-fast=true # Whether to fail fast if the broker is not available on startup.
I want to use ZooKeeper in order to synchronize my distributed services via ZooKeeper ephemeral nodes.
The idea is the following - every node in the topology on the startup will create ZooKeeper session and ephemeral nodes. On the node restart or failure, these nodes will disappear.
I'm going to implement it using Spring Boot. Right now I'm in doubt what project and Maven dependency to use in order to have ZooKeeper client autoconfiguration, be able to create ZooKeeper session on the application startup, be able to create from this client - ZooKeeper ephemeral nodes and use ZooKeeper transactions.
Right now I'm looking on Spring Cloud Zookeeper/ but I'm not sure is it a right one for this purpose. Could you please point me to the right Spring Boot ZooKeeper project and show the small example how to achieve that I have described above.
I use spring cloud config bus (rabbitmq) in my micro-service. Only purpose for me to use rabbitmq in my microservice is spring cloud bus... I have 2 questions below.
When I was experimenting, I found that spring expects rabbitmq to be UP and running during application start. Which is contrary to what Spring cloud evangelises... (Circuit breakers...) To be fair, even service discovery is not expected to be up and running before starting an application. Is there any sensible reason behind this...?
Say, I start my application when rabbitmq is up and running. For some reason, rabbitmq goes down... What I should be losing is just my ability to work with rabbitmq... instead, /health endpoint responds back as DOWN for my micro-service. Any eureka instance listening to heart beats from my micro-service is also marking the instance as down. Any reasons for doing this...?
To my knowledge, this is against the circuit breaker pattern that spring cloud has evangelised.
I personally feel that spring cloud config bus is not an important feature to mark an application as down...
Is there any alternatives to tell my spring boot micro-service that connection to rabbitmq is not a critical service?
Thanks in advance!