XrootD gateway architecture review (What should the XrootD access to Echo look like in a year’s time) | | /wiki/spaces/GRIDPP/pages/255262851 Ideas on xrootd batch farm architecture Current State
ECHO aliases  Key questions:
Should we segregate s3 and WN traffic from FTS?
having each service have its own redirector endpoint is good to maintain high availability and redundancy. additional hardware capacity can then be more easily added to each service if needed.
Shared servers: cmsd allows multiple clusters (redirector managers) to include the same server (gw in our case)
Multiple clusters? with or w/o shared servers? (no shared servers if possible)
[aim to ]Having multiple clusters is good (each service should have its own redirector managers for HA), shared servers will not be needed on a containerised setup, ease of management is preferred over slight resource optimization (with shared servers, underutilised servers could get traffic from other services which are under higher load to make more use of existing capacity) What to aim for: every service instance needs to be as resilient as possible.
each DNS endpoint should have keepalived for redundancy and redirectors for high availability manageability
adding/removing gateways from a service should be simple and the overall setup should not be too complex to understand or manage aim for simpler config
keep the config understandable flexibility on gw/use case to meet burst demand
we should be able to swap add gws between quickly to service endpoints as smoothly as possible to facilitate burst demands (e.g. alice) and to deploy additional capacity quickly
Containerizing everything (shared containers across all hardware) is the preferred desired end state.
This has the prerequisite of every service being behind an expandable high availability setup (xrootd cmsd managers)
[and an orchestrated setup to spin up more gws for load increase] some system resource overhead should be reserved to keep the gateways running smoothly WN gateways:
this should be kept going forwards as they mean we have an additional gateway’s worth of capacity for every workernode.
They currently only redirect traffic for reads over root (job operations using the xrootd.echo endpoint).
This is because of Xcache, which is read only.
Xcache is good at what it does and reduces the number of iops hitting ceph from reads. During the vector read deployment they were removed and resulted in enough IOps to slow down the echo storage cluster enough to fail xcache can be removed if xrdceph buffers provide similar functionality (allows R/W over local gw)
xrdeph buffers do not work on out of order reads or separate read requests (like the case with alice gateways) some sort of xrootd manager tree setup might work for WN gw containers
this could be similar to CMS AAA, with a hierarchy for access, but the first point of contact should be highly available a single gw failing on a workernode should not cause all its jobs to fail. currently there is no failover built in for WN reads, so if the gateway is down all jobs on that WN will fail a functional test equivalent healthcheck for WN gw will ensure the gateway is killed and restarted, and makes condor know if the gateway is still down. This would stop new jobs being sent to a WN with a broken gw but the jobs currently on it will still run. The solution should strongly prefer a WN’s own gw. Ideally there should be some fallback mechanism where the transfer attempts to use its own gateway first and fails over to its neighbour WNs' gateway if unavailable. cmsd is not smart enough to deal with r only and r/w servers as part of its cluster (this was attempted by Sam at Glasgow during early 5.x) strong preference for having the same endpoint for reads and writes (removing xcache). This makes the configuration simpler and allows it to be managed by a cmsd redirector without issues.
A: evaluate whether xcache can be removed with xrdceph buffers enabled (measure IOps on single WN) A: design a better solution for the gws on the WNs A: create redirector managers for alice and s3 A: develop cmsd redirector capability to redirect onto own gateway preferably and have xcaches be included in the redirector in a mixed gw setup
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