Fedora Debuginfod Service - SOP
One virtual machine in prod NFS-mount the koji build system’s RPM
repository, read-only. The production VM has a virtual twin in the
staging environment. They each run elfutils debuginfod to index
designated RPMs into a large local sqlite database. They answers HTTP
queries received from users on the Internet via reverse-proxies at the
https://debuginfod.fedoraproject.org/ URL. The reverse proxies apply
gzip compression on the data and provide redirection of the root
location only into the fedora wiki.
Normally, it is autonomous and needs no maintenance. It should come back nicely after many kinds of outage. The software is based on elfutils in Fedora, but may occasionally track a custom COPR build with backported patches from future elfutils versions.
The daemon uses systemd and
/etc/sysconfig/debuginfod to set basic
parameters. These have been tuned from the distro defaults via
experimental hand-editing or ansible. Key parameters are:
The -I/-X include/exclude regexes. These tell debuginfod what fedora versions to include RPMs for. If index disk space starts to run low, one can eliminate some older fedoras from the index to free up space (after the next groom cycle).
The --fdcache related parameters. These tell debuginfod how much data to cache from RPMs. (Some debuginfo files - kernel, llvm, gtkweb, …) are huge and worth retaining instead of repeated extracting.) This is straight disk space vs. time tradeoff.
The -t (scan interval) parameter. Scanning lets an index get bigger, as new RPMs in koji are examined and their contents indexed. Each pass takes a bunch of hours to traverse the entire koji NFS directory structure to fstat() everything for newness or change. A smaller scan interval lets debuginfod react quicker to koji builds coming into existence, but increases load on the NFS server. More -n (scan threads) may help the indexing process go faster, if the networking fabric & NFS server are underloaded.
The -g (groom interval) parameter. Grooming lets an index get smaller, as files removed from koji will be forgotten about. It can be run very intermittently - weekly or less - since it takes many hours and cannot run concurrently with scanning.
systemd restart debuginfod
activates the new settings.
In case of some drastic failure like database corruption or signs of
penetration/abuse, one can shut down the server with systemd, and/or
stop traffic at the incoming proxy configuration level. The index sqlite
/var/cache/debuginfod may be deleted, if necessary, but
keep in mind that it takes days to reindex the relevant parts of koji.
Alternately, with the services stopped, the 150GB+ sqlite database files
may be freely copied between the staging and production servers, if that
helps during disaster recovery.
The debuginfod daemons answer the standard /metrics URL endpoint to serve a variety of operational metrics in prometheus. Important metrics include:
filesys_free_ratio - free space on the filesystems. (These are also monitored via fedora-infra nagios.) If the free space on the database or tmp partition falls low, further indexing or even service may be impacted. Add more disk space if possible, or start eliding older fedora versions from the database via the -I/-X daemon options.
thread_busy - number of busy threads. During indexing, 1-6 threads may be busy for minutes or even days, intermittently. User requests show up as "buildid" (real request) or "buildid-after-you" (deferred duplicate request) labels. If there are more than a handful of "buildid" ones, there may be an overload/abuse underway, in which case it’s time to identify the excessive traffic via the logs and get a temporary iptables block going. Or perhaps there is an outage or slowdown of the koji NFS storage system, in which case there’s not much to do.
error_count. These should be zero or near zero all the time.
The debuginfod daemons produce voluminous logs into the local systemd
journal, whence the traffic moves to the usual fedora-infra log01
/var/log/hosts/debuginfod*/YYYY/MM/DD/messages.log. The lines
related to HTTP GET identify the main webapi traffic, with originating
IP addresses in the XFF: field, and response size and elapsed service
time in the last columns. These can be useful in tracking down possible
Jun 28 22:36:43 debuginfod01 debuginfod: [Mon 28 Jun 2021 10:36:43 PM GMT] (381551/2413727): 10.3.163.75:43776 UA:elfutils/0.185,Linux/x86_64,fedora/35 XFF:*elided* GET /buildid/90910c1963bbcf700c0c0c06ee3bf4c5cc831d3a/debuginfo 200 335440 0+0ms
The lines related to prometheus /metrics are usually no big deal.
The log also includes info about errors and indexing progress. Interesting may be the lines like:
Jun 28 22:36:43 debuginfod01 debuginfod: [Mon 28 Jun 2021 10:36:43 PM GMT] (381551/2413727): serving fdcache archive /mnt/fedora_koji_prod/koji/packages/valgrind/3.17.0/3.fc35/x86_64/valgrind-3.17.0-3.fc35.x86_64.rpm file /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so
which identify the file names derived from requests (which RPMs the buildids to). These can provide some indirect distro telemetry: what packages and binaries are being debugged and for which architectures?
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