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Placements

A placement puts extra work on a few hosts of a large group without naming them: it picks a number of online hosts, per value of a spread label if set, and gives them a label that layers select. Typical uses are network probes on a few notebooks per office or journey runners spread over zones. How candidates are chosen and replaced is described in Placement.

1. Check the picks​

Fleet › Placements shows each placement with what it wants and what it got:

The netprobe placement: wanted, picked hosts, candidates and shortfall per office zoneThe netprobe placement: wanted, picked hosts, candidates and shortfall per office zone
The netprobe placement wants two notebooks per office zone. ① the Munich office has one candidate only, ② the spec file.

The header names the owner team, the label the placement sets and its spec file ②. Per spread value the table shows:

  • Wanted: the placement's count.
  • Picked hosts: the hosts carrying the placement's label, each linking to its host page.
  • Candidates: the hosts that could be picked; which hosts qualify is described in Placement.
  • Shortfall: how many hosts are missing. With fewer candidates than wanted, all candidates are picked and the rest shows as short ①; adding hosts to the group closes the gap without a change.

stratactl placements prints the same (stratactl placements).

2. See a pick on the host​

A picked host carries the placement's label with the source placement ①, and its host page names the placement and spread value that picked it ②:

The host nb-0002: the role label from the placement and the placement that picked itThe host nb-0002: the role label from the placement and the placement that picked it
nb-0002, picked by netprobe for office-ham: ① the label, ② the placement.

Layers select the label like any other, here role=netprobe. A pick or a replacement is a label change: it re-renders the affected agents without a change set or rollout, and the audit log records it. A manual label with the placement's key would hide the pick, so such hosts are not candidates (Hosts and labels).

3. Change a placement​

Placements have no form in the UI: they are spec files of kind Placement, changed through a change set like any other file.

The spec file placements/netprobe.toml with its Edit buttonThe spec file placements/netprobe.toml with its Edit button
The spec file of netprobe with Edit ①.

Open the file from the placement's header or under Spec, then Edit ① opens it in a draft change set (Make your first change). To add a placement, add a new file of kind Placement. A placement takes effect when the change set is merged; the fields among, count, spread, label and grace are described in Placement.