The document says:
Eureka clients tries to talk to Eureka Server in the same zone. If there are problems talking with the server or if the server does not exist in the same zone, the clients fail over to the servers in the other zones.
So I know clients will query servers at the same zone first. But my question is will clients prefer to choose the remote service at the same zone? Different zones could be mapped to different server rooms so RPC across to another zone may bring more network latency.
Same zone first, the load balancing is done using Ribbon.
http://cloud.spring.io/spring-cloud-static/spring-cloud.html#_using_ribbon_with_eureka
By default it will be used to locate a server in the same zone as the
client because the default is a ZonePreferenceServerListFilter.
Related
I am new to Spring Cloud. Currently, I want to build a new micro service based on Spring Cloud. It is very easy to build a new Eureka server. But my question is that how to make it high availability ? For example I create two Eureka server and a load balancer. When one of the Eureka server is down, the system still works well. But I don't know to to consist registered information in the two Eureka server.
I have already asked something similar in the spring cloud gitter channel.
Because of the CAP theorem, something as a distributes Service discovery has to decide, either to provide availability, or more consistency, with a trade off to the other one.
in short, by quoting Spencer Gibb:
Eureka favors availability over consistency
so it is very available, while registred services may be not acutal anymore.
As Spencer suggested, if consistency is something you need more then availability, try Consul together with spring cloud consul intead
I have my website on Bluemix and all of yesterday they EU region was down. I want to know if it is possible to have another instance on US or Sydney and then, if one is down, automatically redirect to the next.
The platform doesn't have such a feature to automatically redirect to applications in other regions on error conditions. Applications in other regions are treated as separate applications.
Optimally, to handle rare conditions like the one this weekend, you can create a load balancer with something like NGINX or HAProxy outside of bluemix to direct to the best/available geography.
For example: https://www.howtoforge.com/high-availability-load-balancer-haproxy-heartbeat-debian-etch
It has been necessary for IBM to re-start its Bluemix servers this weekend due to an urgent security patch. The IBM recommendation is to take advantage of the capability to have multiple application instances deployed in the different regions, as indicated in Ram's answer.
The maintenance phase in the EU-GB and Sydney regions is now complete. It is ongoing for the US region. For the latest updates and details on this maintenance, check http://ibm.biz/bluemixstatus.
In order to integrate the Vennam response, you could create a load balancer in bluemix using containers (or VM) (of course this workaround doesn't work if containers are down) but you can install NGINX or HAProxy. You could also use Bluemix containers as environment test before moving your load balancer on outside server.
We are setting up a MongoDB replica set on Amazon EC2 in the us-west-1 region.
This region only has two availability zones though. My understanding is that MongoDB must have a majority to work correctly. If we create 2 servers in zone us-west-1b and one server in us-west-1c this will not provide high availability if the entire us-west-1b goes down right? How is this possible? What is the recommended configuration?
Having faced a similar challenge we looked at a number of possible solutions:
Put an Arbiter in another region:
Secure the connection either by using a point to point VPN between the regions a routing the traffic across this connection.
or
Give each server an E-IP and DNS name and use some combination of AWS security groups, IPTables and SSL to ensure connections are secure.
AWS actually have a whitepaper on this not sure how old it is though http://media.amazonwebservices.com/AWS_NoSQL_MongoDB.pdf
Alternatively you could allow the application to fall back to a read-only state until your servers come back on-line (not the nicest of options though)
Hope this helps
I am testing the reliability of TCP connections using Amazon Elastic Load Balancer compared to not using the Load Balancer to see if it has any impact.
I have setup a small Elastic Load Balancer on Amazon EC2 us-east zones with 8 t2.micro instances using an auto scaling group without policy and set to 8 min/max instance.
Each instance run a simple TCP server that accept connections on port 8017 and relay some data to the clients coming from another remote server located in my network. The same data is send to all clients.
For the purpose of the test, the servers running on the micro instances are only sending 1 byte of data every 60 seconds (to be sure the connection don't time out).
I connected multiple clients from various outside networks using the ELB DNS name provided, and after maybe 6-24 hours, I always stop receiving data and eventually the connections all die.
All clients stops around the same time, even though they are on different network/ISP. Each "client" application is doing about 10 TCP connections and they all stop receiving data.
All server instances look fine after this happen, they still send data.
To do further testing and eliminate the TCP server code problem, I also have external clients connected directly to the public IP of a single instance, without the ELB, and the data doesn't stop and the connection is not lost in this case (so far).
The Load balancer Idle Timeout is set to 900 seconds.
The Cross-Zone load balancing is enabled and I am using the following zones: us-east-1e, us-east-1b, us-east-1c, us-east-1d
I read the documentation, and searched everywhere to see if this is a known behaviour, but I couldn't find any clear answer or confirmation of others having the same issue, but it seems clear it is happening in my case.
My question: Is this a known/expected behaviour for TCP load balancer? Otherwise, any idea what could be the problem in my setup?
When we have a cluster of machines behind a load balancer (lb), generally hardware load balancer have persistent connections,
Now when we need to deploy some update on all machines (rolling update), the way to do is by bringing one machine Out of rotation, looks for no request sent to that server via lb. When the app reached no request state then update manually.
With 70-80 servers in picture this becomes very painful.
Can someone have a better way of doing it.
70-80 servers is a very horizontally scaled implementation... good job! Better is a very relative term, hopefully one of these suggestions count as "better".
Implement an intelligent health check for the application with the ability to adjust the health check while the application is running. What we do is have the health check start failing while the application is running just fine. This allows the load balancer to automatically take the system out of rotation. Our stop scripts query the load balancer to make sure that it is out of rotation and then shuts down normally which allows the existing connections to drain.
Batch multiple groups of systems together. I am assuming that you have 70 servers to handle peak load. This means that you should be able to restart several at a time. A standard way to do this is to implement a simple token granting service with a maximum of 10 tokens. Have your shutdown scripts checkout a token before continuing.
Another way to do this is with blue/green deploys. That means that you have an entire second server farm and then once the second server farm is updated switch load balancing to point to the new server farm.
This is an alternate to option 3. Install both versions of the app on the same servers and then have an internal proxy service (like haproxy) switch the connections between the version of the app that is deployed. For example:
haproxy listening on 8080
app version 0.1 listening on 9001
app version 0.2 listening on 9002
Once you are happy with the deploy of app version 0.2 switch haproxy to send traffic to 9002. When you release version 0.3 then switch load balancing back to 9001 etc.