For a cloud instance that runs Apache, I'm guessing the cloud has an IP address.
One of the benefits of using a cloud is scaling, but I'm not sure how that scaling happens. I thought that new instances are created automatically to accommodate rise in traffic. IF that's correct (correct me if I'm wrong), then does that mean that each new instance would have its own IP or what? because if that's the case, it would complicate matters a lot when pointing a domain to a cloud.
The cloud sits behind a load balancer which is able to redirect traffic to different spawned instances of Apache servers. In that since you can grow and shrink to any number of servers based on how much traffic you are receiving.
Related
I got a mail from amazon s3 webservices stating below details
"We are writing to you today to let you know about changes which impact your use of the Amazon Simple Storage Service (S3). In efforts to best serve our customers, we have improved the systems powering the Amazon S3 API and are in the process of shutting down legacy application server capacity. We have detected access on the legacy capacity for Amazon S3 buckets that you own. The legacy capacity is no longer in service, as the DNS entry for the S3 endpoint no longer includes the IP addresses associated with it. We will be shutting down the legacy capacity and retiring the set of IP addresses fronting this capacity after April 1, 2020."
I want to find out which legacy system I am using, and how to prevent from affecting my services.
Imagine you had a web site, www.example.com.
In DNS, that name was pointed to your web server at 203.0.113.100.
You decide to buy a new web server, and you give it a new IP address, let's say 203.0.113.222.
You update the DNS for example.com to point to 203.0.113.222. Within seconds, traffic starts arriving at the new server. Over the coming minutes, more and more traffic arrives at the new server, and less and less arrives at the old server.
Yet, for some strange reason, a few of your site's prior visitors are still hitting that old server. You check the DNS and it's correct. Days go by, then weeks, and somehow a few visitors who used your old server before the cutover are still hitting it.
How is that possible?
That's the gist of the communication here from AWS. They see your traffic arriving on unexpected S3 server IP addresses, for no reason that they can explain.
You're trying to connect to the right endpoint -- that's not the issue -- the problem is that for some reason you have somehow "cached" (using the term in a very imprecise sense) an old DNS lookup and are accessing a bucket by hitting a wrong, old S3 IP address.
If you have a Java backend service accessing S3, those can notorious for holding on to DNS lookups forever. You might need to restart that service, and look into how to resolve that issue and enable correct behavior which is -- as I understand it -- not how Java behaves by default. (Not claiming to be a Java expert but I've encountered this sort of DNS behavior many times.)
If you have an HAProxy or Nginx server that's front-ending for an S3 bucket and has been up for a while, those might need a restart and you should look into how to correctly configure them not to resolve DNS only at startup. I ran into exactly this issue once, years ago, except my HAProxy was forwarding requests to Amazon CloudFront on only 1 of the several IP addresses it could have been using. They took that CloudFront edge server offline, or it failed, or whatever, and the DNS was updated... but my proxy was not able to re-query DNS so it just kept trying and failing until I restarted it. Then I fixed it so that it periodically repeated the DNS lookup so it always had a current address.
If you have your own DNS resolver servers, you might want to verify that they aren't somehow misbehaving, and you might want to ensure that you don't for some reason have any /etc/hosts (or equivalent) static host entried for anything related to S3.
There could be any number of causes but I'm confident at least in my interpretation of what they say is happening.
Is there a way to make physical F5 BigIP LB to route traffic to both EC2 instances(Autoscaling) and physical machines? I came across this article https://devcentral.f5.com/articles/using-big-ip-gtm-to-integrate-with-amazon-web-services but it seems it is routing traffic to an entire AWS zone, not to a couple of EC2 instances behind a ELB.
yes, you can route traffic to any resources from BIG-IP, whether they are locally defined on the same L3 network or remote, you just need to make sure you have routes defined on BIG-IP pointing in the right direction. If you are trying to cloudburst, you can define priority level in the pool so that your physical servers get the traffic unless the minimum threshold is crossed, at which point the remote servers (other datacenter or cloud servers, doesn't matter) will be automatically engaged.
You can also add orchestration to where your cloud servers aren't up and active unless you are getting close to a threshold, at which point the BIG-IP can trigger an action to spin up those servers, then add them to the pool dynamically. There are many options available to you with BIG-IP
Does anyone know how AWS ELB with SSL work behind the scenes? Running an nslookup on my ELB's domain name I get 4 unique IP addresses. If my ELB is SSL enabled, is it possible for AWS to share these same IPs with other SSL enabled ELBs (not necessarily owned by me)?
As I understand it the hostname in a web request is inside of the encrypted web request for a https request. If this is the case, does AWS have to give each SSL-enabled ELB unique IP addresses that are never shared with anyone else's SSL ELB instance? Put another way -- does AWS give 4 unique IP addresses for every SSL ELB you've requested?
Does anyone know how AWS ELB with SSL work behind the scenes? [...] Put another way --
does AWS give 4 unique IP addresses for every SSL ELB you've
requested?
Elastic Load Balancing (ELB) employs a scalable architecture in itself, meaning the number of unique IP addresses assigned to your ELB does in fact vary depending on the capacity needs and respective scaling activities of your ELB, see section Scaling Elastic Load Balancers within Best Practices in Evaluating Elastic Load Balancing (which provides a pretty detailed explanation of the Architecture of the Elastic Load Balancing Service and How It Works):
The controller will also monitor the load balancers and manage the
capacity [...]. It increases
capacity by utilizing either larger resources (resources with higher
performance characteristics) or more individual resources. The Elastic
Load Balancing service will update the Domain Name System (DNS) record
of the load balancer when it scales so that the new resources have
their respective IP addresses registered in DNS. The DNS record that
is created includes a Time-to-Live (TTL) setting of 60 seconds,[...]. By default, Elastic Load Balancing will return multiple IP
addresses when clients perform a DNS resolution, with the records
being randomly ordered [...]. As the traffic
profile changes, the controller service will scale the load balancers
to handle more requests, scaling equally in all Availability Zones. [emphasis mine]
This is further detailed in section DNS Resolution, including an important tip for load testing an ELB setup:
When Elastic Load Balancing scales, it updates the DNS record with the
new list of IP addresses. [...] It is critical that you factor this
changing DNS record into your tests. If you do not ensure that DNS is
re-resolved or use multiple test clients to simulate increased load,
the test may continue to hit a single IP address when Elastic Load
Balancing has actually allocated many more IP addresses. [emphasis mine]
The entire topic is explored in much more detail within Shlomo Swidler's excellent analysis The “Elastic” in “Elastic Load Balancing”: ELB Elasticity and How to Test it, which meanwhile refers to the aforementioned Best Practices in Evaluating Elastic Load Balancing by AWS as well, basically confirming his analysis but lacking the illustrative step by step samples Shlomo provides.
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