Things you need to know while using Burstable instances in AWS!
Be aware of the baseline average CPU performance limits and CPU credit earning rates if you are using the burstable instances such as- t2, t3, t3a, t4g types in AWS due to their low cost offerings!
For example, let's say you chose a t2.medium instance with 2 vCPUs and 4 GB RAM for the Back-End of a moderate size video sharing platform. The price calculator for Oregon region suggests that you'll need to pay approximately $ 35/month.
Now, if you've just started out and the number of server requests is within the range of a few hundreds per hour then it would be fine. But, if your site gets some traction or maybe you are running some campaigns to attract new users rapidly, your server load will increase. In such cases, you might get surprised at the end of the month with the Elastic Compute bill for burstable instances!
Let's analyze the following situation with a t2.medium instance-
According to AWS, it earns 24 CPU credits per hour and it's maximum accruable credit limit is 576.
Now, 1 CPU credit is 100% utilization of 1 vCPU for 1 minute.Thus, the baseline average vCPU utilization for a t2.medium instance is- 24/(60 x 2) which is 20%.
If average vCPU utilization is greater than 20%, it'll start using the accrued credits. For a max limit of 576, it'll provide roughly- 576/(60x2) or 5.8 hours of above baseline usage without any cost.
After the credits are exhausted, additional $0.05/hour (for Linux) will be charged for each vCPUs (for t2.medium it's 2).
Current hourly cost for a t2.medium instance in Oregon region is $ 0.0464 per hour. Thus, if your server is operating above 20% average vCPU utilization continuously for a month in t2 unlimited mode, you might get a monthly bill of- $ (0.0464 + 0.05x2) x (24 x 30) which is around $106 !
For that price, you could use a c5.large instance with much better performance!
In another case, if t2 unlimited mode isn't enabled, average vCPU utilization will be throttled to maintain the baseline performance after the CPU credits are exhausted. So, the UX of the application users will be hampered and as a business owner you don't want that to happen.
Burstable instances could be significantly cost effective if the application server is operating just under the baseline CPU performance most of the time with some occasional spikes. Some of the examples for such applications are-
- Personal Websites/Blogs
- Demo for MVP
- Initial deployment of e-commerce sites and application Back-Ends
- Staging/Testing servers
- Analytical Dashboards for internal use
- CMS/Monitoring Panels
In those cases, one can take advantage of the burstable instances of AWS. Know your customers and their behavior to assess probable server requirements. Don't waste your money on infrastructures that generate no value! Cause making money is so damn hard you know!
Here are the official documentation links:
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