On clarifying t2 and t3 working conditions?

Solution 1:

CPU Credits

There a few key concepts to understand:

1. Each instance continuously earns CPU credits at a constant rate.
2. When the CPU runs (as in not being idle) it spends credits.

Credits are accounted with millisecond precision - if you burst CPU usage for a fraction of a second you'll spend a fraction of a credit.

There is also a concept of baseline performance:

• Below baseline performance the instance spends less credits than it earns so the credit balance keeps going up.
• Above baseline it spends more then it earns and eventually will run out of credits in which case it will be restricted to the baseline performance (because there it earns and spends at the same rate).

The instance will run fast for as long as it's got credits available - i.e. to answer your question: it doesn't take any time to boost. If you've got credits you can run fast.

To get the most benefits AWS recommends to use AMIs with the appropriate virtualisation drivers that advise the host when the instance has nothing to do. Most HVM AMIs should do.

For more info have a look here: https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/burstable-credits-baseline-concepts.html - it provides a very good explanation.

T2/T3 Unlimited

Sometimes you need a fast processing for a period of time that's longer than your CPU Credit balance allows but still relatively short and bursty, so it doesn't warrant using e.g. M4/M5 instead.

For example a source code building instance - runs only a few times per day but may be running for an hour at a time. You don't want to run out of credits and slow down the build half way through, but you also don't want to pay for M4/M5 that will be sitting idle most of the time.

That's where T2/T3 Unlimited comes in - it gives you the benefits of a cheaper price comparing to M4/M5 when idle but can run just as fast.

Again the same two concepts of earning and spending as described above apply, however when you spend all your earned credits instead of slowing down AWS starts charging you for the credits needed to run your instance at full speed, if you don't have any earned ones.

Be aware though that running Unlimited instance at full speed for a long period will be more expensive than using M5. But for some workloads it's a perfect fit.

Hope that helps :)