We Keep Coding

Purpose of Service Discovery such as Eureka

I don’t understand the reasoning behind service discovery tools. I understand they are used so micro services can connect but why can’t we just store all the urls/load balancers in the config server as properties? Looking for some explanation for eureka over property file with the micro service urls.
Thanks

In your example of putting a URL into a config, clients still needs to do discovery to find other micro services . In this case DNS is acting like a discovery service by converting URLs into IP Addresses (to the load balancer).
using a load balancer as state is "server side load balancing" in which a consumer sends a message to the load balancer and the load balancer sends it to the appropriate back end, in this example the load balancer can become a bottle neck on a very busy service.
An alternative is that the clients do their own load balancing by having a list of instances and choosing which ones to send it to based on reports of how busy certain instances are.
Both of these solutions have strengths and weaknesses, but a discovery service such as Eureka are required for the client side load balancing approach.
Services such as eureka often have other nice non-technical advantages, which DNS does not.
The ability to record metadata against a service such as, which team in the company owns it, what it does.
A central place to look up services when you are developing a new service.
Some discovery services can track which services are looking up other services making it easy to do dependency analysis to work out what might break if a service is changed.
If the load balancer/DNS approach is working for you, a dedicated discovery service like Eureka might not fit your architecture.

Discovery service such as Eureka is used for registry purpose so that client can get the address from the registry prior to making a call to the service so if your architecture fits the model where a client based load balancer is favored, Eureka can be a best fit for that. It's norm in microservices that each service can have multiple instances running at a moment for handling the load.
why can’t we just store all the urls in the config server as
properties?
If you put the address of the services in the property file of config server, how you'll register the address of another instance of the same service at run time and make a call to it. For scalability purpose you need to run more than one instance of service, so it is necessary to have discovery service where varying number (1...N) of instances of individual service get them registered and make themselves available to the clients with the help of discovery service. Of course, you've to use some orchestration service such as Kubernetes to handle how many instances you want to run for the service.

spring boot Enterprise application with eureka and zuul

I am in charge of designing a new enterprise application that should handle tons of clients and should be completely fault free.
In order to to that I'm thinking about implementing different microservices that are going to be replicated so eureka server / client solution is perfect for this.
Then since the eureka server could be the single point of failure I found that is possible to have it replicated in multiple instances and it is perfect.
In order to not expose every service I'm going to put as a gateway zuul that will use the eureka server in order to find the perfect instance of the backend serivice that will handle the requests.
Since now zuul is the single point of faiulre I found that it is possible to replicate also this component so if one of them fails I still have the others.
At this point I need to find the way to create a load balancer between the client application (android and ios app) and the zuul stack but a server side load balancer will be the single point of failure so it is useless.
I would like to ask if there is a way to make our tons of clients connect to an healty instance of zuul application without having any single point of failure. Maybe by implementing ribbon on the mobile application that will choose a proper healty instance of zuul.
Unfortunatly everything will be deployed on a "private" cluster so I can not use amazon elastic load balancer or any other different propietary solution
Thanks

Microservices : Without Service Discovery With Spring API Gateway

I'm having a really tough time with this one. We want to move our legacy app to Microservice application(Spring-boot, Java 8) .
As per Architect, we do-not need Service Disvovery and API Gateway is enough for the doing Service Discovery and Routing.
Note that currently , deployments are On premise server and we will have fixed number of nodes and F5/load balancer will be able to route the request to API gateway and then to the microservices.
Can we survive with Spring Cloud API Gateway and no Service Discovery?

A short answer Yes, you can survive with Spring Cloud API Gateway and no Service Discovery.
But it's really dependent on the size of your application and the amount of traffic it will be handling.
You can start migration to microservices without Service discovery.
For internal service-to-service communication just use real hardcoded IP addresses and ports.
Regarding to the API Gateway doing Service Discovery. I can be wrong, but you won't be able to communicate through Api Gateway because it also has no clue about the location of the targets (services locations have to be hardcoded as well).
Once you begin feeling that you need scaling out you won't avoid using Service Registry tool. If you start considering which one to take I can suggest using HashiCorp Consul.
Anyway, it's most likely that you finally will have to inject Service discovery mechanism to your infrastructure. You can either do it from the beginning or take care of it later if the new architecture will be beneficial to you and there will be a plan of extending it further.
If you have plans of migration to the clouds then you can think about Kubernetes for your infrastructure in advance. It provides you with Service discovery mechanism out of the box.

Kubernetes is a great platform for this, if you can opt.
It can handle parts ranging from service discovery to deployment.
You just need to make a cloud ready docker image (preferably) and deploy it to kubernetes, Kubernetes will map an internal endpoint to this, based on your configuration and your services will be registered with it ( if I talk in terms of spring-cloud and eureka server).

If there is no Service-Registry-backed DiscoveryClient then you can configure spring.cloud.discovery.client.simple.instances.userservice[0].uri=http://s11:8080
You can host this userservice on kubernetes cluster .For further details go to this docs
https://cloud.spring.io/spring-cloud-commons/2.2.x/reference/html/
Like wise to have communcation between sevices ,suppose userservice wants to communicate to password service easily configure via ribbon
passwordservice.ribbon.listOfServers:${PASSWORDSERIVCE}:http://localhost:8081
I do not see any problem with this strcuture .

Combination of Spring Cloud and Orchestration Tools Like Docker Swarm and Kubernetes

I have a cloud-native application, which is implemented using Spring Cloud Netflix.
So, in my application, I'm using Eureka service discovery to manage all instances of different services of the application. When each service instance wants to talk to another one, it uses Eureka to fetch the required information about the target service (IP and port for example).
The service orchestration can also be achieved using tools like Docker Swarm and Kubernetes, and it looks there are some overlaps between what Eureka does and what Docker Swarm and Kubernetes can do.
For example, Imagine I create a service in Docker Swarm with 5 instances. So, swarm insures that those 5 instances are always up and running. Additionally, each services of the application is sending a periodic heartbeat to the Eureka internally, to show that it's still alive. It seems we have two layers of health check here, one for Docker and another inside the Spring Cloud itself.
Or for example, you can expose a port for a service across the entire swarm, which eliminates some of the needs to have a service discovery (the ports are always apparent). Another example could be load balancing performed by the routing mesh inside the docker, and the load balancing happening internally by Ribbon component or Eureka itself. In this case, having a hardware load balancer, leads us to a 3-layered load balancing functionality.
So, I want to know is it rational to use these tools together? It seems using a combination of these technologies increases the complexity of the application very much and may be redundant.
Thank you for reading!

If you already have the application working then there's presumably more effort and risk in removing the netflix components than keeping them. There's an argument that if you could remove e.g. eureka then you wouldn't need to maintain it and it would be one less thing to upgrade. But that might not justify the effort and it also depends on whether you are using it for anything that might not be fulfilled by the orchestration tool.
For example, if you're connecting to services that are not set up as load-balanced ('headless services') then you might want ribbon within your services. (You could do this using tools in the spring cloud kubernetes incubator project or its fabric8 equivalent.) Another situation to be mindful of is when you're connecting to external services (i.e. services outside the kubernetes cluster) - then you might want to add load-balancing or rate limiting and ribbon/hystrix would be an option. It will depend on how nuanced your requirements for load-balancing or rate-limiting are.
You've asked specifically about netflix but it's worth stating clearly that spring cloud includes other components and not just netflix ones. And that there's other areas of overlap where you would need to make choices.
I've focused on Kubernetes rather than docker swarm partly because that's what I know best and partly because that's what I believe to be the current direction of travel for the industry - on this you should note that kubernetes is available within docker EE. I guess you've read many comparison articles but https://hackernoon.com/a-kubernetes-guide-for-docker-swarm-users-c14c8aa266cc might be particularly interesting to you.

You are correct in that it does seem redundant. From personal observations, I think that each layer of that architecture should handle load balancing in its' own specific way. It ends up giving you a lot more flexibility for not much more cost. If you want to take advantage of client side load balancing and any failover features, it makes sense to have Eureka. The major benefit is that if you don't want to take advantage of all of the features, you don't have to.
The container orchestration level load balancing has a place for any applications or services that do not conform to your service discovery piece that resides at the application level (Eureka).
The hardware load balancer provides another level that allows for load balancing outside of your container orchestrator.
The specific use case that I ran into was on AWS for a Kubernetes cluster with Traefik and Eureka with Spring Cloud.

Yes, you are correct. We have a similar Spring Cloud Netflix application deployed on Oracle cloud platform and Predix Cloud Foundry. If you use multiple Kubernetes clusters then you have to use Ribbon load balancing because you have multiple instance for services.
I cannot tell you which is better Kubernetes or Docker Swarm. We use Kubernetes for service orchestration as it provides more flexibility.

Best practice to map webservice endpoint in client

this question is more of a design/architecture question. Let's say I have a server application that provides Spring-based webservices and a client application. So currently I have a few Java classes on the client side where the endpoint of the service is hardcoded (e.g. http://myserver/some/webservice).
What is a good way to map the client side properly with the webservice? Just off the top of my head: is there a library that helps evaluate URLs with parameters and maps them to the properties of a POJO using reflection?

As I understand your question, 2 options pop into my head:
1) Eureka- Service Discovery for Spring Cloud.
It can help you by giving your client the Eureka URL and the Eureka will supply the client with the desired service URL. so if there the server is going down Eureka can point the client to a back up server (it will be seamless to the client) or even different URL's to different services on the same server.
2) Spring Cloud Config
A configuration service that contains the URL's in the DB, the client will pull those URLs from there and will make the calls to a configurable URI's.
Spring allow you to update those URL's in the DB and it will use spring cloud config to push the new URL's down to the clients without any downtime... (might fit you better if you are not interested in load balancing and other features provided by Eureka)