[HN Gopher] Decoding AWS Reserved Instances
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Decoding AWS Reserved Instances
Author : abuggia
Score : 40 points
Date : 2022-08-29 15:30 UTC (7 hours ago)
(HTM) web link (blog.symops.com)
(TXT) w3m dump (blog.symops.com)
| londons_explore wrote:
| Reserved instances are effectively a financial construct.
|
| A lot of human hours go into managing them, buying them, selling
| them, making sure they are efficiently used, etc.
|
| I do wonder if the human effort invested in such things is
| actually a net gain over a fixed price. Clearly there is gain for
| the companies using RI's, but is there gain for the economy as a
| whole?
| simonebrunozzi wrote:
| > Reserved instances are effectively a financial construct.
|
| Almost true. It's also a powerful lock-in mechanism.
| jeffwask wrote:
| This is written from an interesting angle and I'm not sure who it
| is meant to serve. It "and then's" Savings Plans but for the
| majority Saving Plans replace RI and are infinitely more flexible
| and easy to use.
|
| TLDR if you are choosing RI's over Saving Plans the basic info
| conveyed in this article is probably already know if you don't
| you should probably just be choosing saving plans.
| scarytom wrote:
| It is great to see articles like this, as Reserved Instances are
| a fantastic way to save some money, and they are widely
| misunderstood.
|
| I work for a company [0] that specialises in Cloud FinOps, and I
| helped write our in-house billing system, which has to deal with
| _all_ of the intricacies of Reserved Instances, so I know very
| well how deep this rabbit hole goes.
|
| This article opens by categorising RIs as "one of the most
| complex but crucial AWS offerings", but I think it perhaps
| glosses over some of that complexity, which might cause people to
| get burnt. For example, it suggests that you can safely sell your
| way out of trouble on the RI Marketplace, but in many cases you
| can't: there are 5 products you can buy RIs for (EC2, RDS,
| ElastiCache, OpenSearch, and Redshift), but the RI Marketplace
| only lets you sell EC2 RIs, and only Standard EC2 RIs at that,
| not Convertible.
|
| I don't want to take anything away from this article, nor do I
| want to frighten people away from buying RIs, but please take
| care. If you aren't sure, I encourage you to use one of the many
| companies operating in this space to help you out (and you
| certainly don't have to give away 20% of your savings to do
| that).
|
| 0: https://strategic-blue.com
| jaywalk wrote:
| Azure's Reservations are far superior. Whether you pay up front
| or monthly doesn't change the cost (there's no "interest") and
| you can cancel the reservation early without this "marketplace"
| nonsense.
|
| It makes Reservations a no-brainer on Azure. The pitfalls with
| AWS make it a little more murky.
| gabagool wrote:
| > Reserved Instances are a major piece of AWS Billing, accounting
| for $100B in revenue along side Saving Plans (SPs).
|
| I think I know what you mean, but this reads like Reserved
| Instances earn AWS $100 billion/year which is almost impossible.
| I don't even think AWS earns that much annually.
| dougb5 wrote:
| This year some of my RIs became useless to me with a chunk of the
| 3-year term remaining, due to the EC2-Classic shutdown. (The
| instance types were a couple of generations old, and no longer
| available in the same availability zones in the VPC network.)
| Since understandably no one on the marketplace wanted to buy
| them, I asked AWS to credit me for the unused time on the RIs,
| with a promise that I'd spend the credit on new RIs on the latest
| generation hardware. They kept saying no -- RIs are a commitment,
| even if they become worthless due to their own mandates,
| apparently. I spent 40 days on a support ticket in which they'd
| go silent for a week at a time and then come back with an offer
| for a credit conditioned on me committing to buy way more RIs
| than I need. Finally they just bought my unused RIs from me on
| the marketplace at their full value. An acceptable outcome, but I
| should never have had to fight AWS for this credit.
| [deleted]
| mrud wrote:
| You should talk to your account manager but for non ec2
| services we have been successful with exchanges by explicitly
| asking for an exchange for a similar/larger amount.
|
| We had to buy the new reservations first and would then could
| cancel the old ones
| BonoboIO wrote:
| No familiar with AWS. So you got Reserved Instance Credis that
| are only able to specific Instances, but the Instances were no
| longer available to "buy".
|
| If that, it is insane that you have to fight that they give you
| your money back.
| efitz wrote:
| It probably would have been better if AWS had called them
| "reservations" rather than "reserved instances".
|
| NB they would never call it a lease or rental because those terms
| have legal repercussions in some jurisdictions.
|
| A reserved instance is simply pre-paying for a specific amount of
| EC2. AWS is able to discount this because: 1. You're pre-paying
| 2. You might not use all the resources you're entitled to, if you
| don't keep a running EC2 instance "filling" the reserved instance
| slot. 3. You're helping them with capacity planning and capacity
| management; there's no guesswork involved with your workload.
| boulos wrote:
| Disclosure: I used to work on GCE.
|
| We got to go second, but I prefer the naming and separation of
| concerns we came up with (obviously): Reservations are capacity
| you're holding, while Commitments are things that get you
| discounts.
|
| Reservations are things your operations team uses to guarantee
| capacity for scaling up, doing rolling restarts, and whatever
| else. Commitments (and Committed Use Discounts) are primarily
| what your Finance teams work with.
|
| The original Reserved Instance product combined both of these.
| AWS now has the same decoupling with Savings Plans and
| Reservations as related, separate products.
| epberry wrote:
| Cool to see Vantage mentioned here! I work for them, mainly on
| the ec2instances.info site.
|
| https://docs.vantage.sh/autopilot/ has many details on how our RI
| management program works. We recently added Autopilot Controls
| which lets you specify categories of instances (like c5) or
| regions that you want managed.
|
| One note on buybacks: they are usually capped. I believe most
| providers cap their "guarantee" around $20K.
| cebert wrote:
| I didn't know this page existed, but nice work. I like how you
| display this data and make is so easy to do comparisons. This
| is a great resource.
| jedberg wrote:
| This article talks about the financial pros and cons of reserved
| instances, but not the important operational benefit:
|
| You will always get an instance when you need it, and never get
| an error about not having enough instances of a certain type.
|
| This is critical if you are using autoscaling, especially during
| an outage. If you are shifting your workload from one region to
| another at the same time as everyone else, if you have
| reservations and they don't, you'll get the instances before
| anyone else.
|
| It breaks the whole "pay as you go" cloud model, but as long as
| you can find batch jobs to fill those reserved instances 1/3 of
| the time, you'll still come out ahead.
| jsmith45 wrote:
| That actually depends.
|
| Reserved instances have one form with zero operation benefits:
| Regional Reserved Instances. These are 100% purely billing
| constructs.
|
| They have zonal Reserved Instances which do reserve capacity.
|
| Finally they have pure capacity reservations. These cost full
| price. Esentially you are paying for an instance even if it is
| not running, but it does guarentee it will be there if you need
| it. but it also has no comittments.
|
| However combining the capacity reservation with a savings plan
| allows you to basically recreate the net effect of a zonal
| Reserved Instance but with additional flexibility.
|
| Regional Reserved Instance's discount will also apply to
| reserved capacity if there were not enough actual instances to
| cover the Reserved Instances.
| rescbr wrote:
| > However combining the capacity reservation with a savings
| plan allows you to basically recreate the net effect of a
| zonal Reserved Instance but with additional flexibility.
|
| This is something that has never crossed my mind. TIL.
| scarytom wrote:
| That used to be true, when AWS only sold AZ-specific RIs, but
| for a long time now AWS have (by default) sold region-level RIs
| instead, and these do not include a capacity reservation. You
| can now purchase Capacity Reservations [0] on their own.
|
| https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ec2-capa...
| vosper wrote:
| > Businesses can sell RIs they've purchased, setting their own
| price for the remainder of the contract.
|
| You can't sell convertible RIs, I thought? Would love to find out
| that's wrong.
|
| From what I've seen RIs are a trap, suitable to hardly anyone,
| especially not startups. If your infra is elastic or evolving at
| all, be really careful before going for RIs. And I would never go
| for more than a one year reserve.
|
| (maybe if you are deploying K8s over RIs it's fine, you'll be
| able to utilise at least partially even if your infra changes -
| but if you have workload-per-instance or service-per-instance
| then be careful)
| scarytom wrote:
| You are correct, you cannot sell Convertible RIs on the RI
| Marketplace.
|
| I think it is going too far to say that RIs are a trap: the
| rules are pretty transparent. I agree with you that if your
| infra is elastic or evolving then you need to be very cautious
| about making large or long-term commitments.
| vosper wrote:
| I think the convertibles are a bit of a trap, though - even
| though the rules are transparent. You might overprovision to
| begin with (which you may not realise), then you can't even
| sell them.
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(page generated 2022-08-29 23:01 UTC)