Wiser coders than myself have come to the conclusion that a `switch`
statement is almost always superior to a statement that includes any
`else if`.
The exceptions that I have found in our codebase are just these two:
* The `if else` is followed by an additional statement before the next
condition (separated by a `;`).
* The whole thing is within a `for` loop and `break` statements are
used. In this case, using `switch` would require tagging the `for`
loop, which probably tips the balance.
Why are `switch` statements more readable?
For one, fewer curly braces. But more importantly, the conditions all
have the same alignment, so the whole thing follows the natural flow
of going down a list of conditions. With `else if`, in contrast, all
conditions but the first are "hidden" behind `} else if `, harder to
spot and (for no good reason) presented differently from the first
condition.
I'm sure the aforemention wise coders can list even more reasons.
In any case, I like it so much that I have found myself recommending
it in code reviews. I would like to make it a habit in our code base,
without making it a hard requirement that we would test on the CI. But
for that, there has to be a role model, so this commit eliminates all
`if else` occurrences, unless it is autogenerated code or fits one of
the exceptions above.
Signed-off-by: beorn7 <beorn@grafana.com>
* Update go to 1.19, set min version to 1.18
Signed-off-by: Julien Pivotto <roidelapluie@o11y.eu>
* Update golangci-lint
Signed-off-by: Julien Pivotto <roidelapluie@o11y.eu>
Signed-off-by: Julien Pivotto <roidelapluie@o11y.eu>
It's currently possible to use blackbox_exporter to probe MX records
themselves. However it's not possible to do an end-to-end test, like is
possible with SRV records. This makes it possible to use MX records as a
source of hostnames in the same way as SRV records.
Signed-off-by: David Leadbeater <dgl@dgl.cx>
This also fixes a bug in query_log_file, which now is relative to the config file like all other paths.
Signed-off-by: Andy Bursavich <abursavich@gmail.com>
i) Uses the more idiomatic Wrap and Wrapf methods for creating nested errors.
ii) Fixes some incorrect usages of fmt.Errorf where the error messages don't have any formatting directives.
iii) Does away with the use of fmt package for errors in favour of pkg/errors
Signed-off-by: tariqibrahim <tariq181290@gmail.com>
* discovery: factorize for SD based on refresh
Signed-off-by: Simon Pasquier <spasquie@redhat.com>
* discovery: use common metrics for refresh
Signed-off-by: Simon Pasquier <spasquie@redhat.com>
https://github.com/miekg/dns/pull/815 goes into the detail, but more or
less the existing solution was no longer supported and needed to be
rewritten to support the new versions of the library. miekg additionally
claims this is more correct in the ticket.
Signed-off-by: Erik Hollensbe <github@hollensbe.org>
Removing a final dot changes the meaning of the name and can cause
extra DNS lookups as the resolver traverses its search path.
Signed-off-by: Bryan Boreham <bjboreham@gmail.com>
Based on https://groups.google.com/d/topic/prometheus-users/02kezHbuea4/discussion
Does not attempt to handle a situation where the server does not understand
EDNS0, however that is an unlikely case, and the behaviour of such ancient
systems is hard to predict in advance, so if it does come up, it will need
to be handled on a case-by-case basis.
* refactor: move targetGroup struct and CheckOverflow() to their own package
* refactor: move auth and security related structs to a utility package, fix import error in utility package
* refactor: Azure SD, remove SD struct from config
* refactor: DNS SD, remove SD struct from config into dns package
* refactor: ec2 SD, move SD struct from config into the ec2 package
* refactor: file SD, move SD struct from config to file discovery package
* refactor: gce, move SD struct from config to gce discovery package
* refactor: move HTTPClientConfig and URL into util/config, fix import error in httputil
* refactor: consul, move SD struct from config into consul discovery package
* refactor: marathon, move SD struct from config into marathon discovery package
* refactor: triton, move SD struct from config to triton discovery package, fix test
* refactor: zookeeper, move SD structs from config to zookeeper discovery package
* refactor: openstack, remove SD struct from config, move into openstack discovery package
* refactor: kubernetes, move SD struct from config into kubernetes discovery package
* refactor: notifier, use targetgroup package instead of config
* refactor: tests for file, marathon, triton SD - use targetgroup package instead of config.TargetGroup
* refactor: retrieval, use targetgroup package instead of config.TargetGroup
* refactor: storage, use config util package
* refactor: discovery manager, use targetgroup package instead of config.TargetGroup
* refactor: use HTTPClient and TLS config from configUtil instead of config
* refactor: tests, use targetgroup package instead of config.TargetGroup
* refactor: fix tagetgroup.Group pointers that were removed by mistake
* refactor: openstack, kubernetes: drop prefixes
* refactor: remove import aliases forced due to vscode bug
* refactor: move main SD struct out of config into discovery/config
* refactor: rename configUtil to config_util
* refactor: rename yamlUtil to yaml_config
* refactor: kubernetes, remove prefixes
* refactor: move the TargetGroup package to discovery/
* refactor: fix order of imports
The problem reported in #2799 was that in the event that all records for a
name were removed, the target group was never updated to be the "empty" set.
Essentially, whatever Prometheus last saw as a non-empty list of targets
would stay that way forever (or at least until Prometheus restarted...). This
came about because of a fairly naive interpretation of what a valid-looking
DNS response actually looked like -- essentially, the only valid DNS responses
were ones that had a non-empty record list. That's fine as long as your
config always lists only target names which have non-empty record sets; if
your environment happens to legitimately have empty record sets sometimes,
all hell breaks loose (otherwise-cleanly shutdown systems trigger up==0 alerts,
for instance).
This patch is a refactoring of the DNS lookup behaviour that maintains
existing behaviour with regard to search paths, but correctly handles empty
and non-existent record sets.
RFC1034 s4.3.1 says there's three ways a recursive DNS server can respond:
1. Here is your answer (possibly an empty answer, because of the way DNS
considers all records for a name, regardless of type, when deciding
whether the name exists).
2. There is no spoon (the name you asked for definitely does not exist).
3. I am a teapot (something has gone terribly wrong).
Situations 1 and 2 are fine and dandy; whatever the answer is (empty or
otherwise) is the list of targets. If something has gone wrong, then we
shouldn't go updating the target list because we don't really *know* what
the target list should be.
Multiple DNS servers to query is a straightforward augmentation; if you get
an error, then try the next server in the list, until you get an answer or
run out servers to ask. Only if *all* the servers return errors should you
return an error to the calling code.
Where things get complicated is the search path. In order to be able to
confidently say, "this name does not exist anywhere, you can remove all the
targets for this name because it's definitely GORN", at least one server for
*all* the possible names need to return either successful-but-empty
responses, or NXDOMAIN. If any name errors out, then -- since that one
might have been the one where the records came from -- you need to say
"maintain the status quo until we get a known-good response".
It is possible, though unlikely, that a poorly-configured DNS setup (say,
one which had a domain in its search path for which all configured recursive
resolvers respond with REFUSED) could result in the same "stuck" records
problem we're solving here, but the DNS configuration should be fixed in
that case, and there's nothing we can do in Prometheus itself to fix the
problem.
I've tested this patch on a local scratch instance in all the various ways I
can think of:
1. Adding records (targets get scraped)
2. Adding records of a different type
3. Remove records of the requested type, leaving other type records intact
(targets don't get scraped)
4. Remove all records for the name (targets don't get scraped)
5. Shutdown the resolver (targets still get scraped)
There's no automated test suite additions, because there isn't a test suite
for DNS discovery, and I was stretching my Go skills to the limit to make
this happen; mock objects are beyond me.
