How shared hosting is built.
WHAT IT IS
Many customers' sites served from one machine, isolated from each other.
WHAT THE COMPONENTS ARE
A web server, serving many sites Language interpreters, running customer code A database server A mail system A control panel A filesystem with per-account separation
WHAT ISOLATION MUST ACHIEVE
One customer unable to read another's files One customer unable to consume all resources One compromised account unable to reach others
WHAT PROVIDES FILE ISOLATION
Per-account users, with appropriate permissions Restricting how far each account can see in the filesystem
WHAT PROVIDES RESOURCE ISOLATION
Limits on processor, memory, processes and storage operations, per account.
WHY THAT SECOND POINT MATTERS MOST
Without it, one site under load makes every site on the server slow.
WHAT CUSTOMERS EXPERIENCE WITHOUT IT
Intermittent slowness with no explanation, which they attribute to the provider.
WHAT TO MONITOR
Per-account resource use, not merely server totals.
WHAT THAT REVEALS
Which account is causing a problem, immediately.
WHAT TO PLAN
Density: how many accounts per machine, based on measurement.
