NodeUtils: export upcall variables to the environment - #705
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Group source upcalls only support textual substitution of $GROUP,
$NODE, $SOURCE and $CFGDIR. Also export them as environment variables
so shell parameter expansions like ${GROUP:-default} work as users
expect, instead of silently reading the caller's environment.
Signed-off-by: Stephane Thiell <stephane@thiell.com>
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The docs now state it explicitly: exported variables take precedence over any same-named variables from the calling environment. Flagging for the 1.11 release notes as a minor behavior change: upcall commands no longer inherit caller-exported |
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Upcall commands already inherit the caller's full environment. This change simply sets the four substitution variables (
$GROUP,$NODE,$SOURCE,$CFGDIR) in that environment, so shell parameter expansions that are not replaced by the library, like${GROUP:-default}, expand to the same values instead of silently reading whatever the caller exported.$GROUPand$NODEare set empty when they do not apply to the upcall. Textual substitution is unchanged and still happens first, so existing configs behave identically.This makes it easy for a map upcall to support a default when the group name is empty, e.g. for query-backed sources:
Here each Prometheus scrape job is a node group, resolving to the hostnames of its targets:
@prometheus:node_exporterexpands to the nodes scraped by thenode_exporterjob, and@prometheus:(empty group name) expands to the nodes of all jobs (useful for map-only sources, where@prometheus:*cannot work).See #609 for a related earlier discussion (FYI).
Docs updated: groups.conf(5) + sphinx config.
Closes #704