I have explained in my previous blog about saving cost using RI and how we can plan. Let’s looks at the combinations of Runbooks and Reserved instances in this blog to save the cost further. We should be careful to get the cost savings out of this model.
You can power off the VMs in non-production environment to save cost when not in use. You can use the runbooks to schedule the Power on and off of the VMs. The below table will provides an insight on what level of cost saving can be brought using runbooks.
If you power off your VMs after your working hours and holidays you would be saving almost up to 76%. I have placed the 3 VMs in different time duration to explain the RI calculation later in this blog. I considered 22 days in a month which excludes weekends
Table 1 – Saving using Runbooks
However, if you consider public holidays, it would be more savings for sure. The runbooks provide cost savings more than 1-year RI and 3 years RI which are 21% and 34% respectively. This proves that RIs do not suit for your non-production environment because runbooks give you more cost savings than RI. So, you may consider RIs only for the production environment unless you see good amount of usage in the non-production environment.
Let’s look at it if you use combination of both RI and Runbook to bring some additional cost savings.
Table 2 – Saving using Runbooks with RI
It is tough to consider calculations like mentioned in the above table because you need to strictly ensure that the VMs are utilizing only 24 hours and there is no overlap. If there is an overlap, you will be charged extra for that in PAYG model. I considered again 22 days and 8 hours per VM with no overlap on VM running schedules. More than the overlap, we need to ensure that we are utilizing the whole hours of the RI. The above table says that you would get some savings only when you opted for 3 years RI.
Table 3 – More Savings using Runbooks with RI
The above table I used 30 days instead of 22 days which is increasing full utilization of VMs. I would consider using those type of VM for running some batch jobs on non-office hours including holidays and weekends.
As I mentioned above, if you do not utilize the hours, it will not be carry forwarded. Below table shows that you will be charged PAYG even though number of hours are equal in total.
Even though it is difficult plan the way it is described above but it isn’t impossible. If you can save a penny in a day for a VM, you will be saving good amount of money in year for several number of VMs.
Table 4 – Wrong way running the VMs with RI with or without Runbooks
In the above table we bought one RI for Standard_E64_V3 but powered on 3 VMs powered on and power off at the same time. Microsoft will bill you one RI cost and 2x VMs PAYG model because it is overlapping for one RI we have. So you should not consider the above table scenario for RI and Runbook combinations.
Please read my All About RIs to get more details on Reserved Instances.
If you are AWS person, Charanjit Cheema has written blog on converting an AWS on demand EC2 instance RI EC2 Instance.