Mine use case is next:
I run application using Spring Boot 2. I have two Redis servers, SERVER_1 and SERVER_2. I have custom health indicator, that will check if both are up. I will use SERVER_1 by default, both for caching and spring session. In case SERVER_1 goes down(health indicator check) I would like to switch to SERVER_2.
While configure Spring Redis to have two connectors\factories is possible, I wonder if it is possible to swap them on runtime?
UPD: I don't care if SERVER_1 and SERVER_2 share same data. Just need the application to connect to working Redis Server.
Related
Sending emails from Spring Boot is as easy as possible.
spring:
mail:
host: <servername>
Plus some additional configuration and off you go.
We rely on an internal email provider that offers two mail servers. Instead of setting these up behind a load balancer, the consumer has to manage the failover itself.
So far, we have therefore only used one of the two servers via the Spring configuration mentioned above.
If this server has a problem, such as the current one where the TLS certificate has expired 🤦♂️, the Rediness Check in Spring Actuator floods the log file with error messages.
Does anyone have a solution for using multiple mail servers to provide a fallback scenario?
I am creating a spring boot microservice project with intelij IDEA.
Currently I have developed three seperate spring boot rest services as customer service, vehicle service and spring cloud config server. Spring cloud config server is pointing to a github repository.
The issue is sometimes above projects take more than 10 minutes to run and sometimes does't run and give an error message as "failed to check application readystate intellij attached provider for the vm is not found". I have no idea why this happens ?
There are two possible causes:
1. IntelliJ IDEA and the Spring application are running in different JVMs.
There is a bug for IntelliJ IDEA regarding that:
https://youtrack.jetbrains.com/issue/IDEA-210665
Here is short summary:
IntelliJ IDEA uses local JMX connector for retrieving Spring Boot actuator endpoint's data by default. However, it could be impossible to get local JMX connector address via attach api if Spring Boot application and IntelliJ IDEA are run by different JVMs. In this case, add the following lines to VM options of your Spring Boot run configuration:
-Dcom.sun.management.jmxremote.port={some_port}
-Dcom.sun.management.jmxremote.authenticate=false
-Dcom.sun.management.jmxremote.ssl=false
As mentioned in the official Oracle documentation, this configuration is insecure. Any remote user who knows (or guesses) your port number and host name will be able to monitor and control your Java applications and platform.
2. Prolonged time to retrieve local hostname
You can check that time using inetTester. Normally it should take only several milliseconds to complete. If it takes a long time then you can add the hostname returned by inetTester to /etc/hosts file like this:
127.0.0.1 localhost winsky
::1 localhost winsky
I want to make an application like JConsole. Is it possible? If yes, what are the changes need to done at JVM level? I am planning to use Spring-Boot. As per my knowledge, JMX is enabled by default. Do I need to configure anything extra in my Spring-Boot app in order to access the JMXBeans which are exposed by default?
Here I'm not trying to expose any MBean instead I'm trying to access those beans which are already exposed by JVM. How to achieve it?
JConsole is a JMX compliant monitoring and management application. The architecture is quite simple. It's a client-server architecture. Where the client is the Remote application (Example JConsole or the one that you want to build) and the server is the JMX Agent. In your case, you want to build your own client which is possible.
I want to make an application like JConsole. Is it possible?
Yes, it is possible.
If yes, what are the changes need to done at JVM level?
What do you mean by changes at JVM level? You are simply creating a client application that connects to the server (JMX Agent) using a certain protocol. Remote Method Invocation (RMI) is the protocol used by JConsole for the connection to the JMX Agent. If you want to use RMI for communication, you don't have to do anything on the server side. But if you want to use some other protocol for communication, you can define your own Protocol adapter.
As per my knowledge, JMX is enabled by default.
As of Java SE 6 it is. But you can only monitor it locally. For connection from a remote machine, you need to define an RMI port to start listening for incoming connections.
Here I'm not trying to expose any MBean instead I'm trying to access those beans which are already exposed by JVM. How to achieve it?
Please check out the example from this link - Mimicking Out-of-the-Box Management Using the JMX Remote API. It shows you how to create a simple client application that connects to a remote JMX agent and access the MBeans. This should guide you in the right direction.
In my project we have a requirement to run two instances of spring cloud config server so if one instance goes down, other will take care the config server responsibilities.
Currently, you would need to put config server behind a load balancer. It is stateless, so that wouldn't hurt. There is an open issue to configure multiple config server url's in the client, so it could do failover there.
If you are running multiple instances of the config server, you can have them all register themselves in Eureka, and maybe do a lookup to the config server with it's application name via Eureka in all the other microservices. This way, Zuul (and Ribbon) will take care of the load balancing.
Edit:
I guess spencergibb is right. It's best to use a load balancer, for eg: ELB, if you're going to deploy on AWS.
Consider multiple spring-cloud-config-uris for high availability
We've three Spring Boot applications:
Eureka Service
Config Server
Simple Web Service making use of Eureka and Config Server
I've set up the services so that we use a Eureka First Discovery, i.e. the simple web application finds out about the config server from the eureka service.
When started separately (either locally or by starting them as individual docker images) everything is ok, i.e. start config server after discovery service is running, and the Simple web service is started once the config server is running.
When docker-compose is used to start the services, they obviously start at the same time and essentially race to get up and running. This isn't an issue as we've added failFast: true and retry values to the simple web service and also have the docker container restarting so that the simple web service will eventually restart at a time when the discovery service and config server are both running but this doesn't feel optimal.
The unexpected behaviour we noticed was the following:
The simple web service reattempts a number of times to connect to the discovery service. This is sensible and expected
At the same time the simple web service attempts to contact the config server. Because it cannot contact the discovery service, it retries to connect to a config server on localhost, e.g. logs show retries going to http://localhost:8888. This wasn't expected.
The simple web service will eventually successfully connect to the discovery service but the logs show it stills tries to establish communication to the config server by going to http://localhost:8888. Again, this wasn't ideal.
Three questions/observations:
Is it a sensible strategy for the config client to fall back to trying localhost:8888 when it has been configured to use discovery to find the config server?
When the eureka connections is established, should the retry mechanism not now switch to trying the config server endpoint as indicated by Eureka? Essentially putting in higher/longer retry intervals and periods for the config server connection is pointless in this case as it's never going to connect to it if it's looking at localhost so we're better just failing fast.
Are there any properties that can override this behaviour?
I've created a sample github repo that demonstrates this behaviour:
https://github.com/KramKroc/eurekafirstdiscovery/tree/master