ADR036: Recommended database plans
==========================
Context
Current plans
As of 2019-09-03 GOV.UK PaaS offers the following postgres and mysql plans to everyone:
MySql
| service plan | description | free or paid |
|---|---|---|
| tiny-unencrypted-5.7 | 5GB Storage, NOT BACKED UP, Dedicated Instance. MySQL Version 5.7. DB Instance Class: db.t2.micro. | free |
| medium-ha-5.7 | 100GB Storage, Dedicated Instance, Highly Available, Storage Encrypted. MySQL Version 5.7. DB Instance Class: db.m4.large. | paid |
| large-ha-5.7 | 512GB Storage, Dedicated Instance, Highly Available, Storage Encrypted. MySQL Version 5.7. DB Instance Class: db.m4.2xlarge. | paid |
| xlarge-ha-5.7 | 2TB Storage, Dedicated Instance, Highly Available, Storage Encrypted. MySQL Version 5.7. DB Instance Class: db.m4.4xlarge. | paid |
| small-ha-5.7 | 20GB Storage, Dedicated Instance, Highly Available. Storage Encrypted. MySQL Version 5.7. DB Instance Class: db.t2.small. | paid |
| small-5.7 | 20GB Storage, Dedicated Instance, Storage Encrypted. MySQL Version 5.7. DB Instance Class: db.t2.small. | paid |
| medium-5.7 | 100GB Storage, Dedicated Instance, Storage Encrypted. MySQL Version 5.7. DB Instance Class: db.m4.large. | paid |
| large-5.7 | 512GB Storage, Dedicated Instance, Storage Encrypted. MySQL Version 5.7. DB Instance Class: db.m4.2xlarge. | paid |
| xlarge-5.7 | 2TB Storage, Dedicated Instance, Storage Encrypted. MySQL Version 5.7. DB Instance Class: db.m4.4xlarge. | paid |
Postgres
| service plan | description | free or paid |
|---|---|---|
| tiny-unencrypted-9.5 | 5GB Storage, NOT BACKED UP, Dedicated Instance, Max 50 Concurrent Connections. Postgres Version 9.5. DB Instance Class: db.t2.micro. | free |
| medium-ha-9.5 | 100GB Storage, Dedicated Instance, Highly Available, Storage Encrypted, Max 500 Concurrent Connections. Postgres Version 9.5. DB Instance Class: db.m4.large. | paid |
| large-ha-9.5 | 512GB Storage, Dedicated Instance, Highly Available, Storage Encrypted, Max 5000 Concurrent Connections. Postgres Version 9.5. DB Instance Class: db.m4.2xlarge. | paid |
| xlarge-ha-9.5 | 2TB Storage, Dedicated Instance, Highly Available, Storage Encrypted, Max 5000 Concurrent Connections. Postgres Version 9.5. DB Instance Class: db.m4.4xlarge. | paid |
| small-ha-9.5 | 20GB Storage, Dedicated Instance, Highly Available, Storage Encrypted, Max 200 Concurrent Connections. Postgres Version 9.5. DB Instance Class: db.t2.small. | paid |
| small-9.5 | 20GB Storage, Dedicated Instance, Storage Encrypted, Max 200 Concurrent Connections. Postgres Version 9.5. DB Instance Class: db.t2.small. | paid |
| medium-9.5 | 100GB Storage, Dedicated Instance, Storage Encrypted, Max 500 Concurrent Connections. Postgres Version 9.5. DB Instance Class: db.m4.large. | paid |
| large-9.5 | 512GB Storage, Dedicated Instance, Storage Encrypted, Max 5000 Concurrent Connections. Postgres Version 9.5. DB Instance Class: db.m4.2xlarge. | paid |
| xlarge-9.5 | 2TB Storage, Dedicated Instance, Storage Encrypted, Max 5000 Concurrent Connections. Postgres Version 9.5. DB Instance Class: db.m4.4xlarge. | paid |
| tiny-unencrypted-10 | 5GB Storage, NOT BACKED UP, Dedicated Instance, Max 50 Concurrent Connections. Postgres Version 10. DB Instance Class: db.t2.micro. | free |
| small-10 | 20GB Storage, Dedicated Instance, Storage Encrypted, Max 200 Concurrent Connections. Postgres Version 10. DB Instance Class: db.t2.small. | paid |
| small-ha-10 | 20GB Storage, Dedicated Instance, Highly Available, Storage Encrypted, Max 200 Concurrent Connections. Postgres Version 10. DB Instance Class: db.t2.small. | paid |
| medium-10 | 100GB Storage, Dedicated Instance, Storage Encrypted, Max 500 Concurrent Connections. Postgres Version 10. DB Instance Class: db.m4.large. | paid |
| medium-ha-10 | 100GB Storage, Dedicated Instance, Highly Available, Storage Encrypted, Max 500 Concurrent Connections. Postgres Version 10. DB Instance Class: db.m4.large. | paid |
| large-10 | 512GB Storage, Dedicated Instance, Storage Encrypted, Max 5000 Concurrent Connections. Postgres Version 10. DB Instance Class: db.m4.2xlarge. | paid |
| large-ha-10 | 512GB Storage, Dedicated Instance, Highly Available, Storage Encrypted, Max 5000 Concurrent Connections. Postgres Version 10. DB Instance Class: db.m4.2xlarge. | paid |
| xlarge-10 | 2TB Storage, Dedicated Instance, Storage Encrypted, Max 5000 Concurrent Connections. Postgres Version 10. DB Instance Class: db.m4.4xlarge. | paid |
| xlarge-ha-10 | 2TB Storage, Dedicated Instance, Highly Available, Storage Encrypted, Max 5000 Concurrent Connections. Postgres Version 10. DB Instance Class: db.m4.4xlarge. | paid |
Current analysis
In #167839682 we had a look at the usage on our existing databases and concluded that, for the most part, the existing plans are appropriate for current usage. We didn’t identify any databases that could easily have been on a smaller instance size if only it had higher IOPS (which was one hypothesis).
There was some evidence in the form of support tickets that our current small plans don’t have enough IOPS, causing people to prematurely upgrade to mediums. AWS warn you against creating DBs with less than 100G disk due to IOPS restrictions, so it seems sensible that we shouldn’t provided plans smaller than that.
At the moment, prices for postgres 10.5 Tiny, Small and Medium instances are:
| plan | price / month |
|---|---|
| tiny | £12.03 |
| small | £24.50 |
| small-ha | £48.98 |
| medium | £125.94 |
| medium-ha | £251.79 |
If we were to increase the disk size on small instances from the current 2G to 100G, this would cause the small plans to increase roughly as follows (based on Ireland prices):
| plan | price / month |
|---|---|
| tiny | £12.03 |
| small | £34.40 (was £24.50) |
| small-ha | £67.88 (was £48.98) |
| medium | £125.94 |
| medium-ha | £251.79 |
We have about 100 “small” databases, of which 28 are HA and 70 are not. This means if we changed the disk on the existing plans our tenants would have to pay an extra £1,200/month (but on the flip side, they might be able to stick with small plans for longer, because of the better IOPS).
Alternatively we could add a new pair of plans like “small-high-iops” and “small-ha-high-iops”.
This would allow an upgrade path of small -> small-high-iops -> medium, instead of the current
small -> medium, which would avoid people paying for CPU and memory they don’t need.
Separately, we should add support for postgres 11 and mysql 8, which are both supported by RDS now. For these new plans we should use the newest available instance types (so t3 / m5 instead of t2 / m4).
Decision
Create new plans for postgres 11
We should play a story to add the following new plans:
| service plan | summary |
|---|---|
| tiny-unencrypted-11 | 5GB Storage, NOT BACKED UP. DB Instance Class: db.t3.micro. |
| small-11 | 100GB Storage. DB Instance Class: db.t3.small. |
| small-ha-11 | 100GB Storage. DB Instance Class: db.t3.small. |
| medium-11 | 100GB Storage. DB Instance Class: db.m5.large. |
| medium-ha-11 | 100GB Storage. DB Instance Class: db.m5.large. |
| large-11 | 512GB Storage. DB Instance Class: db.m5.2xlarge. |
| large-ha-11 | 512GB Storage. DB Instance Class: db.m5.2xlarge. |
| xlarge-11 | 2TB Storage. DB Instance Class: db.m5.4xlarge. |
| xlarge-ha-11 | 2TB Storage. DB Instance Class: db.m5.4xlarge. |
(note: t3 / m5 instances, small plans have 100G storage instead of 20G)
Create new plans for mysql 8
We should play a story to add the following new plans:
| service plan | summary |
|---|---|
| tiny-unencrypted-8 | 5GB Storage. DB Instance Class: db.t3.micro. |
| small-8 | 100GB Storage. DB Instance Class: db.t3.small. |
| small-ha-8 | 100GB Storage. DB Instance Class: db.t3.small. |
| medium-8 | 100GB Storage. DB Instance Class: db.m5.large. |
| medium-ha-8 | 100GB Storage. DB Instance Class: db.m5.large. |
| large-8 | 512GB Storage. DB Instance Class: db.m5.2xlarge. |
| large-ha-8 | 512GB Storage. DB Instance Class: db.m5.2xlarge. |
| xlarge-8 | 2TB Storage. DB Instance Class: db.m5.4xlarge. |
| xlarge-ha-8 | 2TB Storage. DB Instance Class: db.m5.4xlarge. |
(note: t3 / m5 instances, small plans have 100G storage instead of 20G)
Create new “small-high-iops” and “small-ha-high-iops” plans, for mysql 5.7, postgres 9.5 and 10
We should play a story to add “High IOPS” plans for the existing postgres / mysql versions.
These should have 100G of storage and be on the t3.small instance type (since there’s no reason to
be adding new plans on old instance types).
This story may turn out not to be a priority.
Do not change the instance types for the existing plans
We considered whether to upgrade existing databases to new m5 / t3 instances, or to make it so that new databases on old versions (i.e. postgres 9.5 / 10, mysql 5.7) get latest-generation instance types.
We decided not to do this because it would be tricky to administer the change, and it’s nice to have the new instance types as an incentive for people to upgrade.
Status
Accepted
Consequences
- Small databases for the newer engine versions (postgres 11 / mysql 8) will be more expensive and have more disk.
- Some tenants may be able to stick with small databases for longer before they have to upgrade to the medium plan, saving them money.
- Tenants will be able to get higher performing databases by using the newest engine versions (postgres 11 / mysql 8).
- It will be possible for us to implement “downgrading” from
mediumtosmalldatabases for the new plans in the broker (since they have the same sized disks) - this could save tenants money if they optimise their database usage and discover they could move from amediumto asmall. - We will have 9 to 11 more plans for postgres and mysql.