In the very recent commit 3c0e703 fixing issue #8757, we changed the
default prometheus_address setting in scylla.yaml to "localhost", to
match the default listen_address in the same file. We explained in that
commit how this helped developers who use an unchanged scylla.yaml, and
how it didn't hurt pre-existing users who already had their own scylla.yaml.
However, it was quickly noted by Tzach and Amnon that there is one use case
that was hurt by that fix:
Our existing documentation, such as the installation guide
https://www.scylladb.com/download/?platform=centos ask the user to take
our initial scylla.yaml, and modify listen_address, rpc_address, seeds,
and cluster_name - and that's it. That document - and others - don't
tell the user to also override prometheus_address, so users will likely
forget to do so - and monitoring will not work for them.
So this patch includes a different solution to #8757.
What it does is:
1. The setting of prometheus_address in scylla.yaml is commented out.
2. In config.cc, prometheus_address defaults to empty.
3. In main.cc, if prometheus_address is empty (i.e., was not explicitly
set by the user), the value of listen_address is used instead.
In other words, the idea is that prometheus_address, if not explicitly set
by the user, should default to listen_address - which is the address used
to listen to the internal Scylla inter-node protocol.
Because the documentation already tells the user to set listen_address
and to not leave it set to localhost, setting it will also open up
prometheus, thereby solving #9701. Meanwhile, developers who leave the
default listen_address=localhost will also get prometheus_address=localhost,
so the original #8757 is solved as well. Finally, for users who had an old
scylla.yaml where prometheus_address was explicitly set to something,
this setting will continue to be used. This was also a requirement of
issue #8757.
Fixes#9701.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20211129155201.1000893-1-nyh@scylladb.com>
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