After researching various hosts, I still get the feeling that it is somewhat impossible to get a host that would never go down.
Maybe these hosts employ redundancy, maybe they do not. Either case, how would one display a friendly message to the user along the lines of "BRB". What if your host goes down completely for an hour? You would need a way to tell users you would be back. How do you accomplish that?
I doubt any ISP or hosting provider would do that for you. To archieve that you need very expensive and complicated infrastructure like redundant fail-safe routers and backbones in addition to servers of course - and you need multiple. The concepts like Simple Failover requires DNS updates which take minutes to hours to propagate normally, so it's not a 100% solution either. See a good Joel's article for a related discussion.
If the host is down and you're on a single server, then you are definitely down. This is a limitation of shared hosting... there's not much you can do about it. You can ask your host if you are hosted on multiple servers for redundancy... if so, then you wouldn't have to worry about it.
If you host your own server, then you could maybe get your hands on Simple Failover and maybe have a cheap Virtual Dedicated server that goes UP when your primary goes down.
Ok, every host will have downtime at some point. Your best bet would be to go with someone who has the great customer service that can help get your box back up. 99% of the time when your box goes down its your fault (if you have access to the OS/Apache etc).
The people at Rackspace are awesome for hosting + customer service. The rackspace cloud is great allowing you to create and take down servers instantly. (slicehost is good for persistent boxes charged by month, also owned by rackspace)
As for a way to communicate to your users, i would employ twitter, tumblr, or a hosted blog service. This way if your box goes down you can communicate your message via these services which are most likely on a different host/network.
Related
I'm hosting a web application which should be highly-available. I'm hosting on multiple linodes and using a nodebalancer to distribute the traffic. My question might be stupid simple - but not long ago I was affected by a DDoS hitting the data-center. That made me think how I can be better prepared next time this happens.
The nodebalancer and servers are all in the same datacenter which should, of course, be fixed. But how does one go about doing this? If I have two load balancers in two different data centers - how can I setup the domain to point to both, but ignore the one affected by DDoS? Should I look into the DNS manager? Am I making things too complicated?
Really would appreciate some insights.
Thanks everyone...
You have to look at ways to load balance across datacenters. There's a few ways to do this, each with pros and cons.
If you have a lot of DB calls, running to datacenters HOT can introduce a lot of latency problems. What I would do is as follows.
Have the second datacenter (DC2) be a warm location. It is configured for everything to work and is constantly getting data from the master DB in DC 1, but isn't actively getting traffic.
Use a service like CLoudFlare for their extremely fast DNS switching. Have a service in DC2 that constantly pings the load balancer in DC1 to make sure that everything is up and well. When it has trouble contacting DC1, it can connect to CloudFlare via the API and switch the main 'A' record to point to DC2, in which case it now picks up the traffic.
I forget what CloudFlare calls it but it has a DNS feature that allows you to switch 'A' records almost instantly because the actual IP address given to the public is their own, they just route the traffic for you.
Amazon also have a similar feature with CloudFront I believe.
This plan is costly however as you're running much more infrastructure that rarely gets used. Linode is and will be rolling out more network improvements so hopefully this becomes less necessary.
For more advanced load balancing and HA, you can go with more "cloud" providers but it does come at a cost.
-Ricardo
Developer Evangelist, CircleCI, formally Linode
We have some 20 or so servers in EC2, most are dynamically spawned (scaling groups).
We're looking for a solution to monitor the uptime of our application.
As an added bonus this solution could also extend to actually monitoring the servers involved so its easy to go back in time and see what happened just before a downtime or whatnot.
We're looking for a hosted solution ideally, and it should be easy to scale with it (it needs to somehow dynamically deal with servers being added/removed with no interaction from us).
Anyways, hoping for some recommendations from you guys.
A bit of background ...
We're currently using a custom Nagios setup, its been reduced to basically doing a simple http check now that the servers have become fully dynamic. We've already been using PagerDuty to deliver the pages. It does ok, but for the maintenance cost we could well be using a http check # Server Density of Pingdom.
I've looked briefly at ServerDensity, and it does look promising, I especially like their install mechanism of just dumping their files into your AMI and it takes care of the rest.
I'd like to know what options there are tho before diving deeper into any particular solution.
We use a combination of Server Density for monitoring and PagerDuty for alerting. The two work quite well together.
I'm newbie on AWS, and it has so many products (EC2, Load Balancer, EBS, S3, SimpleDB etc.), and so many docs, that I can't figure out where I must start from.
My goal is to be ready for scalability.
Suppose I want to set up a simple webserver, which access a database in mongolab. I suppose I need one EC2 instance to run it. At this point, do I need something more (EBS, S3, etc.)?
At some point of time, my app has reached enough traffic and I must scale it. I was thinking of starting a new copy (instance) of my EC2 machine. But then it will have another IP. So, how traffic is distributed between both EC2 instances? Is that did automatically? Must I hire a Load Balancer service to distribute the traffic? And then will I have to pay for 2 EC2 instances and 1 LB? At this point, do I need something more (e.g.: Elastic IP)?
Welcome to the club Sony Santos,
AWS is a very powerfull architecture, but with this power comes responsibility. I and presumably many others have learned the hard way building applications using AWS's services.
You ask, where do I start? This is actually a very good question, but you probably won't like my answer. You need to read and do research about all the technologies offered by amazon and even other providers such as Rackspace, GoGrid, Google's Cloud and Azure. Amazon is not easy to get going but its not meant to be really, its focus is more about being very customizable and have a very extensive api. But lets get back to your question.
To run a simple webserver you would need to start an EC2 instance this instance by default runs on a diskdrive called EBS. Essentially an EBS drive is a normal harddrive except that you can do lots of other cool stuff with it like take it off one server and move it to another. S3 is really more of a file storage system its more useful if you have a bunch of images or if you want to store a lot of backups of your databases etc, but its not a requirement for a simple webserver. Just running an EC2 instance is all you need, everything else will happen behind the scenes.
If you app reaches a lot of traffic you have two options. You can scale your machine up by shutting it off and starting it with a larger instance. Generally speaking this is the easiest thing to do, but you'll get to a point where you either cannot handle all the traffic with 1 instance even at the larger size and you'll decide you need two OR you'll want a more fault tolerant application that will still be online in the event of a failure or update.
If you create a second instance you will need to do some form of loadbalancing. I recommend using amazons Elastic Load Balancer as its easy to configure and its integration with the cloud is better than using Round Robin DNS or a application like haproxy. Elastic Load Balancers are not expensive, I believe they cost around $18 / month + data that's passed between the loadbalancer.
But no, you don't need anything else to do scale up your site. 2 EC2 instances and a ELB will do the trick.
Additional questions you didn't ask but probably should have.
How often does an EC2 instance experience hardware failure and crash my server. What can I do if this happens?
It happens frequently, usually in batches. Sometimes I go months without any problems then I will get a few servers crash at a time. But its defiantly something you should plan for I didn't in the beginning and I paid for it. Make sure you create scripts and have backups and a backup plan ready incase your server fails. Be ok with it being down or have a load balanced solution from day 1.
Whats the hardest part about scalabilty?
Testing testing testing testing... Don't ever assume anything. Also be prepared for sudden spikes in your traffic. You have to be prepared for anything if you page goes from 1 to 1000 people over night are you prepared to handle it? Have you tested what you "think" will happen?
Best of luck and have fun... I know I have :)
How would I go about setting up a backup for heroku downtimes set up on a vps like linode? (using nginx/unicorn)
Essentially very simply, but also with a whole world of hurt.
Simply create an instance of your application of said VPS.
Then you need to ensure that you're able to flip your DNS from Heroku to said VPS without waiting for a TTL to expire, or someway of letting the world know your application has moved.
Then figure out a reliable way of ensuring that the code on both environments is exactly the same, and works on both different server setups
Then figure out how you can keep the data up to date in both environments so that when you do need to flip, the data will be the same in both environments.
Then you need to figure out a way to remind yourself to keep this secondary VPS up to date from a server management point of view. Software updates, security patches etc etc.
Then you need to figure out a way that you can notified when Heroku is down 24/7
Then you need to hope that when Heroku is down that Linode isn't
... or just accept that any host will go down, and it can cost a hell of a lot of money to ensure that your site doesn't. To be honest, it's probably better for you to look at some sort of hosting setup that allows redundancy and failover across several locations (which won't be cheap)
There are third party services which provide the ability to keep your site (parts of) up if your server goes down - At least it appears to the user that your site is up but it's not working properly behind the scenes. CloudFlare is one such service. It sits in front of your site/application and performs magic (quite simply). It works with static/dynamic sites - and if your server goes offline then they are able to serve static parts of your site. See http://support.cloudflare.com/kb/what-do-the-various-cloudflare-settings-do/what-does-enabling-cloudflare-offline-browsing-do
I'm considering moving a number of small client sites to an unmanaged VPS hosting provider. I haven't decided which one yet, but my understanding is that they'll give me a base OS install (I'd prefer Debian or Ubuntu), an IP address, a root account, SSH, and that's about it.
Ideally, I would like to create a complete VM image of my configured setup and just ship those bits to the provider. Has anyone had any experience with this? I've seen Jeff talk about something like this in Coding Horror. But I'm not sure if his experience is typical. I suppose it also depends on the type of VM server used by the host.
Also, do such hosts provide reverse-DNS? That's kinda useful for sites that send out e-mails. I know GMail tends to bounce anything originating from a server without it.
Finally, I'd probably need multiple IP addresses as at least a couple of the sites have SSL protection which doesn't work with name-based virtual hosts. Has anyone run into trouble with multiple IPs through VPS? I wouldn't think so, but I've heard whisperings to the contrary.
Slicehost (referral link, if you so choose) offers reverse DNS, multiple IPs ($2/month/IP), Ubuntu/Debian (along with others). The only criteria it doesn't support is the ship-a-VM one, but it does let you clone VMs you've set up in their system via snapshots. You could thus set it up once, then copy that VM as many times as you like.
If that's a sacrifice you're willing to make, I highly recommend them - they've had great customer service the few times I've needed to contact them, decent rates, and a great admin backend.
I like XenPlanet, their prices seem to be comparable, but they also allow you to purchase extras like added disk space. Not sure if they let you buy additional bandwidth.
I have used them for a number of different machines and found their service to be very good.