Comment by everforward
3 hours ago
I work in SRE and the way you describe it would give me pause.
The first is that SRE team size primarily scales with the number of applications and level of support. It does scale with hardware but sublinearly, where number of applications usually scales super linearly. It takes a ton less effort to manage 100 instances of a single app than 1 instance of 100 separate apps (presuming SRE has any support responsibilities for the app). Talking purely in terms of hardware would make me concerned that I’m looking at an impossible task.
The second (which you probably know, but interacts with my next point) is that you never have single person SRE teams because of oncall. Three is basically the minimum, four if you want to avoid oncall burnout.
The last is that I don’t know many SREs (maybe none at all) that are well-versed enough in all the hardware disciplines to manage a footprint the size we’re talking. If each SRE is 4 racks and a minimum team size is 4, that’s 16 racks. You’d need each SRE to be comfortable enough with networking, storage, operating system, compute scheduling (k8s, VMWare, etc) to manage each of those aspects for a 16 rack system. In reality, it’s probably 3 teams, each of them needs 4 members for oncall, so a floor of like 48 racks. Depending on how many applications you run on 48 racks, it might be more SREs that split into more specialized roles (a team for databases, a team for load balancers, etc).
Numbers obviously vary by level of application support. If support ends at the compute layer with not a ton of app-specific config/features, that’s fewer folks. If you want SRE to be able to trace why a particular endpoint is slow right now, that’s more folks.
> The last is that I don’t know many SREs (maybe none at all) that are well-versed enough in all the hardware disciplines to manage a footprint the size we’re talking. If each SRE is 4 racks and a minimum team size is 4, that’s 16 racks. You’d need each SRE to be comfortable enough with networking, storage, operating system, compute scheduling (k8s, VMWare, etc) to manage each of those aspects for a 16 rack system. In reality, it’s probably 3 teams, each of them needs 4 members for oncall, so a floor of like 48 racks. Depending on how many applications you run on 48 racks, it might be more SREs that split into more specialized roles (a team for databases, a team for load balancers, etc).
That's vastly overstating it. You hit nail in the head in previous paragraphs, it's number of apps (or more generally speaking ,environments) that you manage, everything else is secondary.
And that is especially true with modern automation tools. Doubling rack count is big chunk of initial time spent moving hardware of course, but after that there is almost no difference in time spent maintaining them.
In general time per server spent will be smaller because the bigger you grow the more automation you will generally use and some tasks can be grouped together better.
Like, at previous job, server was installed manually, coz it was rare.
At my current job it's just "boot from network, pick the install option, enter the hostname, press enter". Doing whole rack (re)install would take you maybe an hour, everything else in install is automated, you write manifest for one type/role once, test it, and then it doesn't matter whether its' 2 or 20 servers.
If we grew server fleet say 5-fold, we'd hire... one extra person to a team of 3. If number of different application went 5-fold we'd probably had to triple the team size - because there is still some things that can be made more streamlined.
Tasks like "go replace failed drive" might be more common but we usually do it once a week (enough redundancy) for all servers that might've died, if we had 5x the number of servers the time would be nearly the same because getting there dominates the 30s that is needed to replace one.
Noteworthy: the number of apps isn't affected by whether the machines are in your datacenter or Amazon's.
So your definition of SRE is anybody that works on infra?