The documentation explains which socket types use load balancing between connected peers, but it doesn't say how it does the load balancing. I'm curious if it's deterministic and if so, what it's based on (order connected, based on address, some internal hash, etc).
It's a simple list, with round-robin load balancing.
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I have setup a HAproxy load balancer and I have a question is when do I need to switch load balancing algorithm ?
Well this depends on your requirements.
Take a look into the documentation balance to know which algorithm is the right one for your setup.
Maybe the Blog post Test Driving “Power of Two Random Choices” Load Balancing can help you also to understand the balancing algorithms in HAProxy.
You can rewrite the profile of HAProxy to switch.you shoulod only modify the setting items: bakcend->balance, whicn can be roundrobin, source, static-rr, etc.
There is no info provided in atlas document on how to scale it.
Apache atlas is connected to cassandra or hbase in the backend which can scale out ,but I dont know how apache atlas engine ( rest web-service and request processor ) can scale out.
I can install multiple instances of it on different machine and have load balancer in front of it to fan out the request. But would this model help ? Does it do any kind of locking and do db transaction, so that this model would not work.
Does someone know how apache atlas scales out ?
Thanks.
So Apache Atlas runs Kafka as the message queue under the covers, and in my experience, the way they have designed the Kafka queue (consumer group that says you should ONLY have ONE consumer) is the choke point.
Not only that, when you look at the code, the consumer has a poll time for the broker of 1 sec hard coded into the consumer. Put these two together, and that means that if the consumer can't process the messages from the various producers (HIVE, Spark, etc) within that second, the broker then disengages the ONLY consumer, and waits for a non-existent consumer to pick up messages...
I need to design something similar, but this is as far as I have got...
Hope that helps somewhat...
Please refer to this page. http://atlas.apache.org/#/HighAvailability
Atlas does not support actual horizontal scale-out.
All the requests are handled by the 'Active instance'. the 'Passive instances' just forward all the requests to the 'Active instance'.
I want to configure IP Load Balancing service for our VPS. I have got the documentation at http://docs.ovh.ca/en/products-iplb.html#presentation where I can integrate it.
I want to limit the number of requests on each server (S1, S2). How can I achieve this?
Suppose, I want S1 should handle all requests if requests sent to load balancer are less than 3500 per minute.
If requests are greater than 3500 (per minute), then load balancer should forward all extra requests to S2.
Regards,
Just had a look and I believe you won't be able to achieve what you are looking for with the available load balancing algorithm.
If you look at the available ones, you can see five ldb algorithm. I would say from my experience with load balancers (not from OVH) that they should do the following:
First: probably the first real server to reply (with health monitor) will get the query
leastcon: this distributes connections to the server that is currently managing the fewest open connections at the time the new connection request is received.
roundrobin: next connection is given to the next real server in line
source: not sure about this one but I believe you load-balance per src ip. Eg if request is coming from 143.32.Y.Z, send it to server A etc.
uri: I believe it load balances by URI. Typical if you are hosting different webservers.
I would advise to check with OVH what you can do. Typically in those scenario with an F5 load balancer for example, you can configure a simple script for this. Or groups, if the first group fail, we sent the traffic to the second one.
Now a ratio (also called weighted) ldb algo can do the job, not exactly what you want indeed.
Cheers
Thanks for taking time to read my questions.
I am having some basic doubts about the load balanced servers.
I assume that One application is hosted on the two servers, when one server is heavily loaded the load balancer is switching the responsibilities of handling the particular request to another server.
This is how I assumed about the load balancer.
Which is managing and monitoring the load and do all the transfers of requests?
How do the static variables are taken place for processing? For ex: , - I have a variable called as 'totalNumberOfClick'. Which is being incremented whenever we hit the page.
If a GET request is handled by a server and its POST method also should be managed by that server.Right? For Ex: in to- A user is requesting a page for editing, the Asp.Net runtime will create a set of viewstate (which has controlID and its values) and is maintained in the server and client side. When we hit the post button the server is validating the view state and allowing it to into a server and doing other processing.
If the post is getting transferred to another server, how the Runtime allow it to do the processing.
If you are using the load balancing built into Windows, then there are several options for how the load is distributed. The servers keep in communication with each other and organise the load between themselves.
The most scalable option is to evenly balance the requests across all of the servers. This means that each request could end up being processed by a different server so a common practice is to use "sticky sessions". These are tied to the user's IP address, and make sure that all requests from the same user go to the same server.
There is no way to share static variables across multiple servers so you will need to store the value in a database or on another server.
If you find an out of process to host session state (such as stateserver or sql server) then you can process any request on any server. Viewstate allows the server to recreate most of the data needed that generated the page.
I have some answers for you.
When it comes to web applications, load balancers need to provide what is calles Session Stickyness. That means that once a server is elected to serve a clients request all subsequent request will be directed to the same node as long as the session is active. Of course this is not neccessary if your web application does not rely on any state that has to be preserved (i.e. stateless, sessionless).
I think this can answer your third and maybe even your second question.
Your first question is on how load balancers work internally. Since I am not an expert in that I can only guess that the load balancer that each client is talking to measures ping response times to derive an estimated load amount on the server. Maybe more sophisticated techniques could be used.
Hey there guys, I am a recent grad, and looking at a couple jobs I am applying for I see that I need to know things like runtime complexity (straight forward enough), caching (memcached!), and load balancing issues
(no idea on this!!)
So, what kind of load balancing issues and solutions should I try to learn about, or at least be vaguely familiar with for .net or java jobs ?
Googling around gives me things like network load balancing, but wouldn't that usually not be adminstrated by a software developer?
One thing I can think of is session management. By default, whenever you get a session ID, that session ID points to some in-memory data on the server. However, when you use load-balacing, there are multiple servers. What happens when data is stored in the session on machine 1, but for the next request the user is redirected to machine 2? His session data would be lost.
So, you'll have to make sure that either the user gets back to the same machine for every concurrent request ('sticky connection') or you do not use in-proc session state, but out-of-proc session state, where session data is stored in, for example, a database.
There is a concept of load distribution where requests are sprayed across a number of servers (usually with session affinity). Here there is no feedback on how busy any particular server may be, we just rely on statistical sharing of the load. You could view the WebSphere Http plugin in WAS ND as doing this. It actually works pretty well even for substantial web sites
Load balancing tries to be cleverer than that. Where some feedback on the relative load of the servers determines where new requests go. (even then session affinity tends to be treated as higher priority than balancing load). The WebSphere On Demand Router that was originally delivered in XD does this. If you read this article you will see the kind of algorithms used.
You can achieve balancing with network spraying devices, they could consult "agents" running in the servers which give feedback to the sprayer to give a basis for decisions where request should go. Hence even this Hardware-based approach can have a Software element. See Dynamic Feedback Protocol
network combinatorics, max- flow min-cut theorems and their use