Marrying Nginx with ELB

Few weeks back I got a requirement to setup a highly available API server. I said not a big deal! I’ll have Nginx as a reverse proxy(Why not directly exposing API via ELB a different story) and my API auto scaled setup will sit behind an internal ELB and things would be in place TA DA.

Things worked perfectly fine for few days, but one day the API consumer reported that they are not getting response back, what? When I checked the API url was indeed returning a 502 error code. It was really strange for nginx to be sending 502 response back that meant the highly scalable setup was down? Well I was proven wrong ELB was working perfectly fine as the curl request to internal ELB was returning proper response, so yes the highly available API setup was in place. What next, yes! Nginx error logs. I did saw Nginx reporting connection timeout with 502 error code. The interesting thing to note that it was an IP(random IP assigned to ELB), when I tried to do curl hit on that IP for API request, it did failed EUREKA EUREKA!! I reproduced the problem.

Well now I’ve to collect all this information and infer what is the logical cause of the problem, and yes there are lot of smart people available who would have fond the solution to this problem so I’ve to ask right question in Google :). The question was “Nginx using Ip instead of domain name” and the answer was “Nginx caches the IP at the startup and obviously as ELB is Elastic in nature so it’s IP changes over the period of time”. That was the reason Nginx was trying to talk to the older un-associated IP’s of Internal ELB.

Finding solution was not a big task as it was just about making sure  Nginx should talk to ELB not the IP’s associated with it, that’s why said marrying nginx with ELB :).

I’ll not go into the actual solution as there are already solutions available in web. I referred this really good blog as a solution.

http://ghost.thekindof.me/nginx-aws-elb-dns-resolution-nginx-resolver-directive-and-black-magic/

VPC per envrionvment versus Single VPC for all environments

This blog talks about the two possible ways of hosting your infrastructure in Cloud, though it will be more close to hosting on AWS as it is a real life example but this problem can be applied to any cloud infrastructure set-up. I’m just sharing my thoughts and pros & cons of both approaches but I would love to hear from the people reading this blog about their take as well what do they think.

Before jumping right away into the real talk I would like to give a bit of background on how I come up with this blog, I was working with a client in managing his cloud infrastructure where we had 4 environments dev, QA, Pre Production and Production and each environment had close to 20 instances, apart from applications instances there were some admin instances as well such as Icinga for monitoring, logstash for consolidating logs, Graphite Server to view the logs, VPN server to manage access of people.

At this point we got into a discussion that whether the current infrastructure set-up is the right one where we are having a separate VPC per environment or the ideal setup would have been a single VPC and the environments could have been separated by subnet’s i.e a pair of subnet(public private) for each environment

Both approaches had some pros & cons associated with them

Single VPC set-up

Pros:

  1. You only have a single VPC to manage
  2. You can consolidate your admin app’s such as Icinga, VPN server.

Cons:

  1. As you are separating your environments through subnets you need granular access control at your subnet level i.e instances in staging environment should not be allowed to talk to dev environment instances. Similarly you have to control access of people at granular level as well
  2. Scope of human error is high as all the instances will be on same VPC.

VPC per environment setup

Pros:

  1. You have a clear separation between your environments due to separate VPC’s.
  2. You will have finer access control on your environment as the access rules for VPC will effectively be access rules for your environments.
  3. As an admin it gives you a clear picture of your environments and you have an option to clone you complete environment very easily.

Cons:

  1. As mentioned in pros of Single VPC setup you are at some financial loss as you would be duplicating admin application’s across environments

In my opinion the decision of choosing a specific set-up largely depends on the scale of your environment if you have a small or even medium sized environment then you can have your infrastructure set-up as “All environments in single VPC”, in case of large set-up I strongly believe that VPC per environment set-up is the way to go.

Let me know your thoughts and also the points in favour or against of both of these approaches.

How to Manage Amazon Web Services Instances part 1

If you want to minimize the amount of money you spend on Amazon Web Services (AWS) infrastructure, then this blog post is for you. In this post I will be discussing  the rationale behind starting & stopping AWS instances in an automated fashion and more importantly, doing it in a correct way. Obviously you could do it through the web console of AWS as well, but it will need your daily involvement. In addition, you would have to take care of starting/stopping various services running on those instances.

Before directly jumping on how we achieved instance management in an automated fashion, I like to state the problem that we were facing. Our application testing infrastructure is on AWS and it is a multiple components(20+) application distributed among 8-9 Amazon instances. Usually our testing team starts working from 10 am, and continues till 7 pm. Earlier we used to keep our testing infrastructure up for 24 hours, even though we were using it for only 9 hours on weekdays, and not using it at all on weekends. Thus, we were wasting more then 50% of the money that we spent on the AWS infrastructure. The obvious solution to this problem was: we needed an intelligent system that would make sure that our amazon infrastructure was up only during the time when we needed it.

The detailed list of the requirements, and the corresponding things that we did were:

  1. We should shut down our infrastructure instances when we are not using them.
  2. There should be a functionality to bring up the infrastructure manually: We created a group of Jenkins jobs, which were scheduled to run at a specific time to start our infrastructure. Also a set of people have execution access to these jobs to start the infrastructure manually, if the need arises.
  3. We should bring up our infrastructure instances when we need it.
  4. There should be a functionality to shut down the infrastructure manually: We created a group of Jenkins jobs that were scheduled to run at a specific time to shut down our infrastructure. Also a set of people have execution access on these jobs to shut down the infrastructure manually, if the need arises.
  5. Automated application/services start on instance start: We made sure that all the applications and services were up and running when the instance was started.
  6. Automated graceful application/services shut down before instance shut down: We made sure that all the applications and services were gracefully stopped before the instance was shut down, so that there was be no loss of data.
  7. We also had to make sure that all the applications and services should be started as per defined agreed order.

Once we had the requirements ready, implementing them was simple, as Amazon provides a number of APIs to achieve this. We used AWS CLI, and needed to use just 2 simple commands that AWS CLI provides.
The command to start an instance :
aws ec2 start-instances –instance-ids i-XXXXXXXX
The command to stop an instance :
aws ec2 stop-instances –instance-ids i-XXXXXXXX 

Through above commands you can automate starting and stopping AWS instances, but you might not be doing it the correct way. As you didn’t restrict the AWS CLI allow firing of start-instances and stop-instances commands only, you could use other commands and that could turn out to be a problem area. Another important point to consider is that we should restrict the AWS instances on which above commands could be executed, as these commands could be mistakenly run with the instance id of a production amazon instance id as an argument, creating undesirable circumstances 🙂

In the next blog post I will talk about how to start and stop AWS instances in a correct way.

Attach a new volume to EC2 Instance

This blog will talk about how to mount a new volume to an existing EC2 instance, though it is very straightforward & simple, but it’s good to have a checklist ready with you so that you can do things in one go instead of searching here and there. The most important thing to take note of in this blog is that you have to do couple of manual operations apart from mounting the volume through AWS Web UI.

  1. Go to the AWS Volumes screen, create a new volume if not created already.
  2. Select Attach Volume in Actions button
  3. Choose the instance, to which this volume needs to be mounted
  4. Confirm the volume state changes from available to in-use
  5. Go to the AWS Instances screen, select the EC2 instance to which volume was attached
  6. Check the Block Devices in the details section you can see the new volume details their. Let’s say it is mounted at /dev/sdf.
  7. Now log in to the EC2 instance machine, you can’t see the mounted volume yet(it is like an external un-formatted hdd that is connected to a linux box)
  8. To make it usable execute below commands
sudo su –                              [Switch to superuser]
mkfs -t ext3 /dev/xvdf                      [Format the drive if it is a new volume]
mkdir /home/mettl/mongo                      [Simply create a new directory]
mount /dev/xvdf /home/mettl/mongo   [Mount the drive on newly created directory]
Make sure to change permissions according to how you use it.
  1. To mount EBS volumes automatically on startup add an entry in /etc/fstab
/dev/xvdf    /home/mettl/mongo    ext3    defaults,nobootwait,comment=cloudconfig    0    0
Hope you will find this blog useful, rest assured this is the starting point of a new series I would be talking about couple of other best practices such as why do you need to have this kind of setup, how you will upgrade volume in case of a running ec2-instance..

How to securely access your private app on cloud

One of the suggested practices in cloud administration is to always host your applications on a Virtual Private Cloud. Also, you should have a public subnet hosting the public facing apps, and a private subnet which hosts the private apps (like a database or a back-end service/app). To know more about why you need such kind of a setup, please read more about VPC.

This blog will talk about a scenario where you have multiple Virtual Private Clouds (hereafter referred to as VPC), and you need to access a private app hosted in one VPC from another VPC. An example of this scenario could be that you have a VPC for your staging environment and another VPC for production environment, then you’d like to sync the database from of production environment from the staging environment. In this case, it might not be straight forward to do this, as you might not be able to access the production database from outside the production VPC.

One of the solutions for this problem would be to first take a dump of the production database on one of the public facing machines in the production VPC, and then copy that dump to a public facing machine in the Staging VPC and finally applying this dump to the private database of Staging environment. This approach will work, but it would not be a perfect solution, as you have to copy the db dump between VPC’s.

A much better approach would be if you could directly connect to the production database from the Staging VPC & execute the dump & restore command, for that you need direct access of production database from staging environment. This approach is called port-forwarding. We configure port-forwarding at one of the public facing machines(NAT is the preferred one) in the production VPC in such a manner that if a request comes on this machine at port x it will be forwarded to port y on a private facing machine in the production VPC which is the database production in this case.

In the next blog I will talk about other alternate approaches that can be used to solve this problem.