Give an example for --reserve-memory #325
Conversation
Codecov Report
@@ Coverage Diff @@
## master #325 +/- ##
==========================================
- Coverage 48.84% 48.68% -0.16%
==========================================
Files 186 186
Lines 12413 12416 +3
==========================================
- Hits 6063 6045 -18
- Misses 5976 5996 +20
- Partials 374 375 +1 |
| on an approach. | ||
|
|
||
| On Linux, you can also limit a service's overall memory footprint on a given | ||
| host, `cgroups` or other mechanisms at the level of the operating system. |
There was a problem hiding this comment.
I'm having trouble understanding this sentence; I think maybe a word is missing somewhere.
There was a problem hiding this comment.
Yes, "using" is missing.
| schedule a service on a host that doesn't have enough memory. `--limit-memory` | ||
| will limit the service's memory to stay within that limit, so if every service | ||
| has a memory-reservation and limit set, Docker services won't saturate the | ||
| host. |
There was a problem hiding this comment.
I think this over-promises slightly - even if all services have memory reservations and limits, there could still be other non-containerized (or non-service container) software on the host using memory, as you point out earlier, which would cause Docker to exhaust the available memory.
|
Overall this is very good. It's a difficult topic to explain. I think the most important thing to get across is that the scheduler doesn't look at actual measurements of real-time memory use. It only pays attention to the reservations. So there's no magic that makes sure enough memory is available before scheduling a container on a certain host - it's entirely up to the operator to specify reservations, and make sure that the reserved memory will actually be available (for example, by limiting service memory use as well). The text does a good job of explaining this. I would also add special emphasis on the danger of mixing services with reservations and services without reservations. Since a service without a memory reservation doesn't have any memory reserved for it, the scheduler would still be able to schedule that service to a node where all the memory is reserved. If you want to use memory reservations, it's important to use them for all services, otherwise the services without reservations can negate the careful work you did to keep memory usage under control. |
Signed-off-by: Misty Stanley-Jones <misty@docker.com>
|
Addressed feedback. PTAL again. |
| If your service needs a minimum amount of memory in order to run correctly, | ||
| you can use `--reserve-memory` to specify that the service should only be | ||
| scheduled on a node with this much memory available to reserve. If no node is | ||
| available that meets the criteria, the service is not scheduled, but remains in |
There was a problem hiding this comment.
"the task is not scheduled"
|
|
||
| On Linux, you can also limit a service's overall memory footprint on a given | ||
| host at the level of the host operating system, using `cgroups` or other | ||
| relevant operating system tools. |
There was a problem hiding this comment.
Just want to confirm it's possible to do this at the host OS level for a swarm service. ping @crosbymichael @justincormack
There was a problem hiding this comment.
Probably by creating a cgroup, and setting it as parent-cgroup on the daemon
|
Finish this change guys, please. The community have a lot of issues with limiting resources for containers. In the swarm especially. IMO |
|
carried in #2316 |
Carrying moby/moby#32631
Incorporated feedback from that PR.