I am new to AWS. I can't get a clear idea behind ALB vs NLB. Could anyone explain in a simple way?
There are some excellent answers out there already, let me pick out some key points that may help.
Network Load Balancer
As the name implies, this is for the network levels only. Typically layer 4.
It does not care, nor see, about anything regarding the application layer, such as cookies, headers, etc.
It is context-less, caring only about the network-layer information contained within the packets it is directing this way and that.
the 'balancing' done here is done so solely with IP addresses, port numbers, and other network variables.
Application Load Balancer
This takes into account multiple variables, from the application to the network. It can route its traffic based on this.
It is context-aware and can direct requests based on any single variable as easily as it can a combination of variables.
Key Differences
The network load balancer just forward requests whereas the application load balancer examines the contents of the HTTP request header to determine where to route the request
Network load balancing cannot assure availability of the application, where as Application load balancing can.
Some good sources from where I extracted this information are:
https://medium.com/awesome-cloud/aws-difference-between-application-load-balancer-and-network-load-balancer-cb8b6cd296a4
https://linuxacademy.com/community/show/22677-application-load-balancer-vs-network-load-balancer/
https://aws.amazon.com/elasticloadbalancing/features/#compare
In main response by #james above, network level has been defined multiple times and mentions about network layer information. However, I would like to mention, NLB yes operates on Layer4, but Layer4 is Transport Layer not Network Layer. NLB preserves source IP and thus Elastic IP can be used in case of NLB.
Related
I am trying to understand how reverse proxy and load balancing are different from each other. When its useful to use reverse proxy over load balancing.
Both promise to improve efficiency and sits in between client and server. They nearly look the same when we try to understand them, but still their functionality differs.
Load balancing: Is hardware or a software unit that distributes the total load on a website by distributing it to multiple servers.
The algorithms used by load balancing should be chosen as such it makes the best use of each servers’ capacity and can provide the result as fast as possible.
Load balancers are of three categories: DNS Round Robin, L3/L4 Load Balancer [ works on IP and TCP layer ], and L7 Load Balancer [ works on application layer].
The different kinds of algorithms used by load balancer for distributing load are IP Hash, Least connection, Round robin, Least traffic, etc.
Reverse Proxy: They act as a face of website or we can say they serve as a gateway that web traffic has to pass. The main role of a reverse proxy is:
Security: They act as a wall to your backend server. Protecting the backend from direct interactions and thus improving the security of the overall system.
Web acceleration: It also provides features like caching, SSL encryption, and Compression to reduce the time to provide responses to clients.
Flexibility: The changes in backend architecture become more flexible as the client can only access the reverse proxy.
A reverse proxy can even be relevant even when there is only one server in your system. In such cases there is no requirement of load balancers but still the reverse proxy can be useful providing security, flexibility and web acceleration.
According to this link,
A reverse proxy accepts a request from a client, forwards it to a server that can fulfill it, and returns the server’s response to the client. In other words, Reverse proxies act as such for HTTP traffic and application programming interfaces.
A load balancer distributes incoming client requests among a group of servers, in each case returning the response from the selected server to the appropriate client. Load balancers can deal with multiple protocols — HTTP as well as Domain Name System protocol, Simple Message Transfer Protocol and Internet Message Access Protocol. A load balancer receives and routes client requests for application, text, image or video data to any server in a pool that is capable of fulfilling them and then returns the server’s response to the client.
I have 2 geographically separately hosted AEM (adobe experience manager) instances under the same TLD but with separate sub domains.
For example www.foo.com (instance 1) and www2.foo.com (instance 2)
Is it possible to have both these AEM instances appear under the same TLD? For example something like :
www.foo.com/instance1/ and www.foo.com/instance2/
Any help appreciated!
Yes, this sort of thing is done often using network tools. Typically a website that is built to handle a load will have some sort of load balancer in front of it. The load balancer would sit even ahead of the dispatchers in the overall flow. With a load balancer you can specify routing rules (such as an irule with an F5 load balancer) that will cause the load balancer to send traffic to different places based on the rules you set up--such as the differences in the initial folder structure of the URLs. Check out some articles on irules for more background, such as https://devcentral.f5.com/articles/the101-irules-ndash-introduction-to-irules.
The same can also be done via content delivery networks (CDNs). Ultimately, what you are looking to do must be done at some network layer before the request actually hits an AEM server. The AEM instances themselves won't know that other instances exist. They will just respond to the requests that reach them, and it will be up to the routing layers in the network upstream from them to determine which HTTP requests go to which AEM servers.
See also:
http route url parts to different server
server
Forward specific urls on same domain to different servers
I just started learning load balancers. Taking a server side application (http/https) load balancer as an example, I assume it listens a specific ip address, then forward the http requests to available servers based on its algorithm.
So is it possible for a load balancer to become a bottleneck? Because it's listening a specific ip address, all requests will first go to the single load balancer. So I think there could be a scenario where the amount of traffic is beyond the limit/capacity of the load balancer.
When it becomes a bottleneck, what can we do? Can we use multiple load balancers?
I think one possible solution is to use multiple load balancers and expose all the ips to clients. (This sounds like client side load balancing) So when a client wants to send a request, it can pick from the ip pool and then send a request to one of the load balancers. (For example, ZooKeeper could be used here.) Is this a working solution? Is there any other way to use multiple load balancers?
Thanks.
Ethan
Your last suggestion works with adding a little twist: The usual approach is to publish the load balancer IP addresses under the same domain name.
This is called DNS load balancing. Clients will ask for the IP resolution for your load balancer's domain name and they will get different IP addresses on a round-robin fashion.
To configure DNS load balancing you have to add multiple A records for your load balancer's domain name to your DNS configuration. Here you can find an example guide for that.
what's the best way to achieve high availability for a dynamic website? If I create a second copy on another server and do not wish to use a load balancer since it will mess up user sessions, what are the best alternatives?
You can store session data in a database instead, which gets around that problem, then you can round-robin the requests to the application servers.
(Good) Load Balancers can be configured to be "sticky" which means they send requests from the same IP to the same server each time.
Even if you have a load balancer sitting infront of two backend webservers, you just move the single point of failure onto the load balancer instead of the webserver. So your application would still not be highly available.
I highly recommend using a load balancer and at least a pair of web servers. At work, we use HA Proxy, which is fully capable of ensuring sessions are 'sticky', and are sent to the same web server unless it goes down, where it will fail over.
To make your load balancer highly available, you can set up two load balancing servers which are a mirror image of each other. Assign a single virtual IP to both of your load balancers. Write a script that will poll the other server to check if it's down; if it's down, have that script pick up that virtual IP address. The script should be running on both servers.
This link describes one way of managing a virtual IP address. Similar articles have been written for a large number of linux distros, but they are all based on the same method.
Loadbalancers. They should be configured in such a way that they can handle the sessions. Maybe by sending the same ip to the same backend every time. Or store them inside a database, or some shared memory if it needs to be really fast for some reason i haven't thought of.
From what I understand, if you have multiple web servers, then you need some kind of load balancer that will split the traffic amongst your web servers.
Does this mean that the load balancer is the main connecting point on the network? ie. the load balancer has the IP address of the domain name?
If this is the case, it makes it really easy to add new hardware since you don't have to wait for any dns propogation right?
There are several solutions to this "problem".
You could round-robin at the DNS-level. I.e. have www.yourdomain.com point to several IP-addresses (well all your servers).
This doesn't give you any intelligence in the load balancing, but the load will be more or less randomly distributed, but you wouldn't be resilient to hardware failures as they would still require changes to DNS.
On the other hand you could use a proxy or a loadbalancing proxy that has a single IP but then distributes the traffic to several back-end boxes. This gives you a single point of failure (the proxy, you could of course have several proxies to defeat that problem) and would also give you the added bonus of being able to use some metric to divide the load more evenly and intelligently than with just round-robin dns.
This setup can also handle hardware failure in the back-end pretty seamlessly. The end user never sees the back-end, just the front-end.
There are other issues to think about as well, if your page uses sessions or other smart logic, you can run into synchronisation problems when your user (potentially) hits different servers on every access.
It does (in general). It depends on what server OS and software you are using, but in general, you'll hit the load balancer for each request, and the load balancer will then farm out the work according to the scheme you have in place (round robin, least busy, session controlled, application controlled, etc...)
andy has part of the answer, but for true load balancing and high availability you would want to use a pair of hardware load balancers like F5 bigips in an active passive configuration.
Yes your domain IP would be hosted on these devices and traffic would connect firstly to those devices. Bigips offer a lot of added functionality including multiple ways of load balancing and some great url rewriting, ssl acceleration, etc. It also allows you to run your web servers on a seperate non routable address scheme and even run multiple sites on different ports with the F5's handling the translations.
Once you introduce load balancing you may have some other considerations to take into account for your application(s) like sticky sessions and session state but that is a different subject