I'd like to raise this as a general issue for discussion. I am working
with these:
blackbox_exporter, version 0.24.0 (branch: HEAD, revision:
0b0467473916fd9e8526e2635c2a0b1c56011dff)
build user: root@e5bbfcc8184e
build date: 20230516-11:07:25
go version: go1.20.4
platform: linux/amd64
tags: netgo
snmp_exporter, version 0.25.0 (branch: HEAD, revision:
9c42d6c874d479314e612bca69558c81f8e26287)
build user: root@880115266f70
build date: 20231210-10:05:18
go version: go1.21.5
platform: linux/amd64
tags: netgo
In blackbox_exporter, it's inconsistent whether IPv6 literals need to be
enclosed in square brackets or not.
- With the icmp prober, IPv6 literals *must not* be enclosed in brackets
AFAICS
- With the dns prober, IPv6 literals *must not* be enclosed in brackets,
unless you also provide a port. e.g. [::1] is invalid, but [::1]:53 is OK,
as far as I can tell
- With the tcp prober, I don't think the port can be omitted anyway; hence
IPv6 literals *must* be enclosed in brackets and followed by :port
This makes it difficult to write generic code to map a device to a target
plus module, because it depends on what underlying prober the module is
using.
Looking at the wider Prometheus ecosystem:
- Prometheus service discovery requires square brackets, because
__address__ is an address:port combination
- snmp_exporter does *not* allow the square brackets in the target address
if it doesn't have a port. Conversely, you can add the square brackets, but
if you do you *must* add a port; it doesn't add :161 automatically. (This
is like the dns prober in blackbox_exporter)
# curl -vsS
'localhost:9116/snmp?target=[2001:db8::1]&module=mikrotik&auth=workshop_v3'
error collecting metric Desc{fqName: "snmp_error", help: "Error scraping
target", constLabels: {module="mikrotik"}, variableLabels: {}}: error
connecting to target [2001:db8::1]: error establishing connection to host:
dial udp: address [[2001:db8::1]]:161: missing port in address
That looks like a straightforward bug to me: it seems to be attempting to
add the :161 port, but is mangling it with an extra set of brackets.
If that can be fixed (and maybe it's the same issue in dns prober), then it
will be possible to use brackets around IPv6 addresses without ports.
That leaves the icmp prober in blackbox exporter. I think it should allow
square brackets, if not actually require them (there's no useful concept of
"port" here, it will always send an echo-request). It might be more
consistent to require square brackets
P.S. I would expect the blackbox_exporter http prober to require square
brackets around IPv6 literals in URLs, but I can't them to work: e.g.
curl -g
'localhost:9115/probe?target=http:%2f%2f%5b2001:db8::1%5d&module=http_2xx_example'
doesn't make an outbound connection to 2001:db8::1. But quite possibly I'm
doing something wrong.
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