I'm having troubles with the communication between microservices. I have many spring boot applications, and many requests HTTP and AMQP (RabbitMQ) between them. Locally (in dev) I use Eureka (Netflix Oss) without Docker Images.
The question is: in the Amazon ECS Infraestructure how i can work with the same behavior? Which is the common pratice for the communication between microservices using Docker? I can still use Eureka for Service Discovery? Besides that, how this comunication will works between container instances?
I'd suggest reading up on ECS Service Load Balancing, in particular two points:
Your ECS service configuration may say that you let ECS or the EC2 instance essentially pick what port number the service runs on externally. (ie for Spring Boot applications inside the Docker container your application thinks it's running on port 8080, but in reality to anything outside the Docker container it may be running on port 1234
2 ECS clusters will check the health endpoint you defined in the load balancer, and kill / respawn instances of your service that have died
A load balancer gives you different ways to specify which application in the cluster you are talking to. This can be route based or DNS name based (and maybe some others). Thus http://myservice.example.com/api could point to a different ECS service than http://myservice.exaple.com/app... or http://app.myservice.example.com vs http://api.myservice.example.com.
You can configure ECS without a load balancer, I'm unsure how well that will work in this situation.
Now, you're talking service discovery. You can still use Eureka for service discovery, having Spring Boot take care of that. You may need to be clever about how you tell Eureka where your service lives (as the hostname inside the Docker container may be useless, and the port number inside the container totally will be too.) You may need to do something clever here to correctly derive that number, like introspecting using AWS APIs. I think this SO answer describes it correctly, or at least close enough to get started.
Additionally apparently ECS has service discovery built in now. This is either new since I last used ECS, or we didn't use it because we had other solutions. If you aren't completely tied to Eureka for other reasons.
Thanks for you reply. For now I'm using Eureka because I'm using Feign too for comunication between microservices.
My case is this: I have microservices (Example A,B,C). A communicates with B and C by way of Feign (Rest).
Microservices Example
Example of Code on Microservice A:
#FeignClient("b-service")
public interface BFeign {
}
#FeignClient("c-service")
public interface CFeign {
}
Using ECS and ALB it's possible still using Feign? If yes or not, how you suggest I do this?
Related
I have 2 ECS Services running with EC2 launch type and bridge networking mode. each service is having 1 task and both tasks are running on same EC2 container host.
on the Same ECS host, API container in 1st task is trying to communicate DB container in 2nd task by host name and port number( ex: http://abc-def:5000). what are the ways to achieve this ?
Your options are:
Put everything in a single task definition. Then you can use the link attribute to enable container A to communicate with container B like so B:port. Notice that link does not support circular relations meaning if A can talk with B, B will not be able to do that as well.
Switch to network mode host. This way you can communicate with localhost.
Proper service discovery with a tool like Consul or AWS ECS Service Discovery. I have no experience with the latter. See here.
Put your tasks behind ALB and use this load balancer to communicate between tasks.
I have number of java and python services running in docker containers in clustered environment. I'm using Eureka for service discovery and it works fine locally with Eureka ip address hardcoded in application configuration files. I have problem with flexible configuration of Eureka service for Java services - docker containers with the services will be deployed in three environments where Eureka will have different ip addresses.
Is there a way to pass Eureka URI using e.g. JVM environment variable?
Or if I pass the URI as an application argument, how can I get it propagated to the Eureka client configuration?
PS: I use AWS ECS and due to number of services and existing AWS constraints I cannot put all docker containers in a single task definition, cannot use docker names resolving and just hardcode Eureka hostname, on the other hand I might have multiple Eureka instances and would like to specify which one particular container should use.
The answer to this my question would be to use configuration server, description of this beast can be found here https://dzone.com/articles/using-spring-config-server.
I have been working with spring and now would like to learn spring boot and microservices. I understand what microservice is all about and how it works. While going through docs i came across many things used to develop microservices along with spring boot which i am very much confused.
I have listed the systems below.and the questions:
Netflix Eureka - I understand this is service discovery platform.
All services will be registered to eureka server and all
microservices are eureka clients. Now my doubt is , without having
an API gateway is there any use with this service registry ? This is
to understand the actual use of service registry.
ZUULApi gateway- I understand ZUUL can be used as API gateway which is basically a load balancer , that calls appropriate
microservice corresponding to request URL. iS that assumption
correct? will the api gateway interact with Eureka for getting the
appropriate microservice?
NGINX - I have read NGINX can also be used as API gateway? Is that possible? Also i read some where else like NGINX can be used as a service registry , that is as an alternate for Eureka ! Thus which is right? Api gateway or service registry or both? I know nginx is a webserver and reverse proxies can be powerfully configured.
AWS api gateway - Is this can also be used as an alternate for ZUUL?
RIBBON - for what ribbon is used? I didn't understand !
AWS ALB- This can also be used for load balancing. Thus do we need ZUUL if we have AWS ALB?
Please help
without having an API gateway is there any use with this service registry ?
Yes. For example you can use it to locate (IP and port) of all your microservices. This comes in handy for devops type work. For example, at one project I worked on, we used Eureka to find all instances of our microservices and ping them for their status (/health, /info).
I understand ZUUL can be used as API gateway which is basically a load balancer , that calls appropriate microservice corresponding to request URL. iS that assumption correct?
Yes but it can do a lot more. Essentially because Zuul is more of a framework/library that you turn into a microservice, you can code it to implement any kind of routing logic you can come up with. It is very powerful in that sense. For example, lets say you want to change how you route based on time of day or any other external factors, with Zuul you can do it.
will the api gateway interact with Eureka for getting the appropriate microservice?
Yes. You configure Zuul to point to Eureka. It becomes a client to Eureka and even subscribes to Eureka for realtime updates (which instances have joined or left).
I have read NGINX can also be used as API gateway? Also i read some where else like NGINX can be used as a service registry , that is as an alternate for Eureka ! Thus which is right? Api gateway or service registry or both?
Nginx is pretty powerful and can do API gateway type work. But there are some major differences. AFAIK, microservices cannot dynamically register with Nginx, please correct me if I am wrong... as they can with Eureka. Second, while I know Nginx is highly (very highly) configurable, I suspect its configuration abilities do not come close to Zuul's routing capabilities (due to having the whole Java language at your disposal within Zuul to code your routing logic). It could be the case that there are service discovery solutions that work with Nginx. So Nginx will take care of the routing and such, but service discovery will still require a solution.
Is this can also be used as an alternate for ZUUL?
Yes AWS API Gateway can be used as a Zuul replacement of sorts. The issue here, just like Nginx, is service discovery. AWS API Gateway lets you apply logic to your routing... though not as open ended as Zuul.
for what ribbon is used?
While you can use the Ribbon library directly, for the most part consider it as an internal dependency of Zuul. It helps Zuul do the simple load balancing that it does. Please note that this project is in maintenance mode and not recommended any more.
This can also be used for load balancing. Thus do we need ZUUL if we have AWS ALB?
You can use ALB with ECS (elastic container service) to replace Eureka/Zuul. ECS will take care of the service discover for you and will map all instances of a particular service to a Target Group. Your ALB routing table can then route to Target Groups based on simple routing rules. The routing rules in ALB are very simple though, but improving over time.
Different systems which can be used for the working of microservices, that comes along with spring boot:
Eureka:
Probably the first microservice to be UP. Eureka is a service registry, means , it knows which ever microservices are running and in which port. Eureka is deploying as a sperate application and we can use #EnableEurekaServer annotation along with #SpringBootAPplication to make that app a eureka server. So our eureka service registery is UP and running. From now on all microservices will be registered in this eureka server by using #EnableDiscoveryClient annotation along with #SpringBootAPplication in all deployed microservices.
Zuul: ZUUL is a load balancer , routing application and reverse proxy server as well. That is before we were using apache for reverse proxy things , now , for microservices we can use ZUUL. Advantage is, in ZUUL we can programatically set configurations, like if /customer/* comes go to this microservice like that. Also ZUUL can act as a load balancer as well , which will pick the appropriate microservice in a round robin fashion. SO how does the ZUUL knows the details of microservices, the answer is eureka. It will work along with eureka to get microservice details. And in fact this ZUUL is also a Eureka client where we should mark using #EnableDiscoveryClient, thats how these 2 apps(Eureka and zuul) linked.
Ribbbon:
Ribbon use for load balancing. This is already available inside ZUUL, in which zuul is using Ribbon for load balancing stuff. Microservices are identified by service-name in properties file. IF we run 2 instances of one microservices in different port, this will be identified by Eureka and along with Ribbon(Inside zuul), requests will be redirected in a balanced way.
Aws ALB , NGINX , AWS Api gateway etc: There are alternatives for all the above mentioned things. Aws is having own load balancer, service discovery , api gateway etc . Not only AWS all cloud platofrms ,like Azure, have these. Its depends which one to use.
Adding a general question as well , How these microservices communicate each other: Using Resttemplate or Feignclient actual rest API can be called or Message queues like Rabbit MQ etc can be used .
Eureka can be used in conjunction with NGINX, which leads to very powerful combination.
I am using it on AWS EC2 environment. Previously instead of NGINX I was using Spring Cloud Gateway and before that Zuul. Depending of the load Spring Cloud Gateway was running on AWS t3.medium or t3.large instances. After moving to NGINX I am using t3.micro (8 times less memory) instance. I am almost sure that I can do the trick and with t3.nano (16 times less memory) instance, but I wanted to be sure that there will be no surprises.
Below are the high level steps what you have to do in order to plug NGINX in the Eureka ecosystem. More details you can find in NGINX With Eureka Instead of Spring Cloud Gateway or Zuul article.
Create a service which can read the configuration of all applications from Eureka and to 'translate' it to NGINX configuration.
Create a cronjob entry which at certain period will read the configuration from the above service and will call the NGINX hot reload
NGINX which will consume the configuration produced from the service and the cronjob and will work as API Gateway
We are using Eureka with AWS ECS service that can scale docker containers.
In ECS if you leave out the host port, or specify it as being '0', in your task definition, then the port will be chosen automatically and reported back to the service. After the task is running, describing it should show what port(s) it bound to.
How does Eureka can resolve what port to use if we have several EC2 instance. For example Service A from EC2-A try to call Service B from EC2-B. So Eureka can resolve hostname , but cannot identify exposed port
Hi #Aleksandr Filichkin,
I don't think Application Load Balancer and service registry does the same.
The main difference traffic flows over the (application) load balancer whereas the service registry just gives you a healthy endpoint that your client directly can address (so the network traffic does not flow over the service registry).
Cheap is a very relative term, maybe it's cheap for some, maybe it's an unnecessary overhead for others.
The issue was resolved
https://github.com/Netflix/eureka/issues/937
Currently ECS agent knows about running port.
But I don't recommend to use Eureka with ECS, because Application Load Balancer does the same. It works as service registry and discovery. You don't need to run addition service(Eureka), ALB is cheap.
There is another solution.
You can create an application loadbalancer and a target group, in which the docker containers can be launched.
Every docker container has set their hostname to the hostname of the loadbalancer. If you need a pretty url, then you can utilize Route53 for DNS-Routing.
It looks like this:
Service Discovery with Loadbalancer-Hostname
Request Flow
If you have two containers of the same task on different hosts, both will communicate the same loadbalancer hostname to eureka.
With this solution you can use eureka with docker on AWS ECS without loosing the advantages and flexibility of dynamic port mapping.
We are testing the ECS infrastructure to run an application that requires a backend service (a MySQL) as well as a few web servers. Since we'd like to restart and redeploy the front end web servers independently from the elasticsearch service, we were considering defining them as separate task definitions, as suggested here.
However, since the container names are autogenerated by ECS, we have no means of referring to the container running the MySQL instance, and links can only be defined between containers running on the same task.
How can I make a reference to a container from a different task?
PS: I'd like to keep everything running within ECS, and not rely on RDS, at least for now.
What you're asking about is generally called service discovery, and there are a number of different alternatives. ECS has integration with ELB through the service feature, where tasks will be automatically registered in the ELB and deregistered in the ELB appropriately. If you want to avoid ELB, another pattern might be an ambassador container (there's a sample called the ecs-task-kite that uses the ECS API) or you might be interested in an overlay network (Weave has a fairly detailed getting started guide for their solution).