8 Must-read AWS Interview Questions

Here’re eight AWS interview questions asked in top companies. The topics include EBS, S3, IAM, Security, Auto-scaling, and Configuration management.

AWS Interview Questions

1. Explain Elastic Block Storage (EBS)? What type of performance can you expect? How do you back it up? How do you improve performance?

EBS is a virtualized SAN or storage area network. That means it is RAID storage to start with so it’s redundant and fault-tolerant. If disks die in that RAID you don’t lose data.

Great!

It is also virtualized, so you can provision and allocate storage, and attach it to your server with various API calls. No calling the storage expert and asking him or her to run specialized commands from the hardware vendor.

Performance on EBS (Elastic block store) can exhibit variability. That is it can go above the SLA performance level, then drop below it.

The SLA provides you with an average disk I/O rate you can expect. This can frustrate some folks, especially performance experts who expect reliable and consistent disk throughput on a server.

Traditional physically hosted servers behave that way. Virtual AWS instances do not. Back up EBS volumes by using the snapshot facility via an API call or via a GUI interface like an elastic fox.

Improve performance by using Linux software raid and striping across four volumes.

2. What is S3? What is it used for? Should encryption be used?

S3 stands for Simple Storage Service. You can think of it like FTP storage, where you can move files to and from there, but not mount them like a filesystem.

AWS automatically puts your snapshots there, as well as AMIs there. Encryption should be considered for sensitive data, as S3 is a proprietary technology developed by Amazon themselves, and as yet unproven vis-à-vis a security standpoint.

3. What is an AMI? How do I build one?

AMI stands for Amazon Machine Image. It is effectively a snapshot of the root file system.
Commodity hardware servers have a bio that points to the master boot record of the first block on a disk.
A disk image though can sit anywhere physically on a disk, so Linux can boot from an arbitrary location on the EBS storage network.
Build a new AMI by first spinning up an instance from a trusted AMI. Then adding packages and components as required.
Be wary of putting sensitive data onto an AMI. For instance, your access credentials should be added to an instance after spinup.
With a database, mount an outside volume that holds your MySQL data after spinup as well.

4. Can I vertically scale an Amazon instance? How?

Yes. This is an incredible feature of AWS and cloud virtualization. Spin up a new larger instance than the one you are currently running.

Pause that instance and detach the root EBS volume from this server and discard it.

Then stop your live instance, and detach its root volume. Note the unique device ID and attach that root volume to your new server.

And then start it again. Voila, you have scaled vertically in place!!

Cloud Storage Benefits

5. What is auto-scaling? How does it work?

Autoscaling is a feature of AWS which allows you to configure and automatically provision and spin up new instances without the need for your intervention.

You do this by setting thresholds and metrics to monitor. When those thresholds are crossed a new instance of your choosing will be spun up, configured, and rolled into the load balancer pool. Here are AWS white papers to improve further.

6. What automation tools can I use to spin up servers?

The most obvious way is to roll your own scripts and use the AWS API tools. Such scripts could be written in bash, Perl, or another language of your choice.
The next option is to use configuration management and provisioning tools like puppet or better its successor Opscode Chef. You might also look towards a tool like Scalr.
Lastly, you can go with a managed solution such as Rightscale.

7. What is configuration management? Why would I want to use it with cloud provisioning of resources?

Configuration management has been around for a long time in web operations and systems administration.
Yet its cultural popularity of it has been limited. Most systems administrators configure machines as the software was developed before version control – that is manually making changes on servers.
Each server can then and usually is slightly different. Troubleshooting though is straightforward as you log in to the box and operate on it directly.
Configuration management brings a large automation tool into the picture, managing servers like strings of a puppet.
This forces standardization, best practices, and reproducibility as all configs are versioned and managed. It also introduces a new way of working which is the biggest hurdle to its adoption.
Enter the cloud, and configuration management becomes even more critical. That’s because virtual servers such as Amazon EC2 instances are much less reliable than physical ones.
You absolutely need a mechanism to rebuild them as-is at any moment. This pushes best practices like automation, reproducibility, and disaster recovery into center stage.
While on the subject of configuration management take a quick peek at hiring a DevOps guide.

8. Explain how you would simulate perimeter security using the Amazon Web Services model?

Traditional perimeter security that we’re already familiar with using firewalls and so forth is not supported in the Amazon EC2 world.
AWS supports security groups. One can create a security group for a jump box with ssh access – only port 22 is open.
From there a webserver group and database group are created. The webserver group allows 80 and 443 from the world, but port 22 only from the jump box group.
Further, the database group allows port 3306 from the webserver group and port 22 from the jump box group.
Add any machines to the webserver group and they can all hit the database. No one from the world can, and no one can directly ssh to any of your boxes.

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