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Revision as of 23:05, 29 May 2022

Icinga ( http://www.icinga.org/ ) is a host and service monitoring software using a binary daemon, some cgi scripts for the web interface and binaries plugins to check various things. Basically, automated testing of our site that screams and sends up alarms when it fails. It originated as a fork of the earlier project "Nagios", from which WMF transitioned in 2013.

It can be set to monitor services such as ssh, squid status, mysql socket as well as # of user logged in, load, disk usage. There are two levels of alarms (warning, critical) and the notification system is fully customizable (groups of users, notified by email / irc / pager, stop notifying after x alarm...).

Our installation can be found at https://icinga.wikimedia.org which is currently an alias to machine alert1001.

Paging / Alert System Details

Our icinga installation sends pages through VictorOps.

Configuration

Puppet

Puppet is being integrated with Nagios as well, in file manifests/nagios.pp. To monitor the availability of a host, simply define the following anywhere under its node definition (i.e. in site.pp or included classes):

monitor_host { $hostname: }

To monitor a service, e.g. SSH, use something like the following:

monitor_service { "ssh": description => "SSH status", check_command => "check_ssh" }

Custom Checks

Custom checks can be found scattered throughout the operations/puppet git repo. Large concentrations of them can be found in these paths:

Many custom checks send HTTP requests to check the health of services. It's important that such checks follow meta::User-Agent policy to identify their traffic, and so that we don't inadvertently block monitoring requests when we need to shut off / ratelimit harmful bot traffic. The User-Agent sent by Icinga checks should be wmf-icinga/<script_name> (root@wikimedia.org).

Grafana

As of 2020 Grafana alerts with Icinga are deprecated. See grafana alerts with Alertmanager instead.

IRC notification

Icinga appends messages to several different files /var/log/icinga/irc*.log, and ircecho (which runs as a systemd service) maps lines appended there to channels.

Sometimes the bot is wedged and a systemctl restart ircecho will likely fix it.

Updating channels where notifications are sent

  1. Submit a patch changing modules/profile/manifests/icinga/ircbot.pp
  2. Run puppet
  3. The bot will automatically restart on configuration change

Acknowledgement logic

From Nagios Wiki (but this was just on Google Cache and the original site seemed gone, so pasted it here)

  • There is a difference between sticky and non-sticky acknowledgements
From Nagios 3.2.3.

Assuming you have a service with notifications enabled for all states with a max retry attempts of 1, these are the notifications you should get based on the following transitions:

#service in OK
#service goes into WARNING - notification sent
#non-sticky acknowledgement applied
#service goes into CRITICAL. Acknowledgement removed. Notification sent
#non-sticky acknowledgement applied
#service goes into WARNING. Acknowledgement removed. Notification sent
#non-sticky acknowledgement applied
#service goes into CRITICAL. Acknowledgement removed. Notification sent
#service goes into OK. Recovery notification sent 


This is the flow if sticky acknowledgements are used:

#service in OK
#service goes into WARNING - notification sent
#sticky acknowledgement applied
#service goes into CRITICAL. No notification sent
#service goes into WARNING. No notification sent
#service goes into CRITICAL. No notification sent
#service goes into OK. Recovery notification sent 

Scheduling downtimes with a shell command

Modern approach centralized:

  • From one of the cluster management hosts run the sre.hosts.downtime cookbook. See sudo cookbook sre.hosts.downtime -h for all the related info.

Modern approach:

  • Check which is the icinga host (host icinga.wikimedia.org)
  • Ssh to the icinga host, be root or use sudo with the command
  • /usr/local/bin/icinga-downtime -h short-hostname -r "why are you rebooting this host"
This form of the command schedules a downtime of 2 hours
  • Add -d num_seconds if you want to schedule a different length downtime
  • Output from the command will show you that icinga processes downtimes for the host (one log entry) and for all services on that host (second log entry).
  • There is no script for removing downtime, so choose a reasonable length.

Old approach:

Put multiple hosts into a scheduled downtime, from now on for the next 3 days. Example used on Labs Nagios:

nagios command file is a named pipe at /var/lib/nagios/rw/nagios.cmd

for host in huggle-wa-w1 puppet-lucid turnkey-1 pad2 webserver-lcarr asher1 dumpster01 dumps-4 ; do
printf "[%lu] SCHEDULE_HOST_DOWNTIME;$host;$(date +%s);1332479449;1;0;259200;Dzahn;down to save memory on virt3 having RAM issues\n" $(date +%s) \
> /var/lib/nagios/rw/nagios.cmd ; done

After a few seconds you should see something like this in /var/log/icinga/icinga.log (on icinga1001)

[1332220596] HOST DOWNTIME ALERT: dumpster01;STARTED; Host has entered a period of scheduled downtime
Command Format:
SCHEDULE_HOST_DOWNTIME;<host_name>;<start_time>;<end_time>;<fixed>;<trigger_id>;<duration>;<author>;<comment>

quote: If the "fixed" argument is set to one (1), downtime will start and end at the times specified by the "start" and "end" arguments. Otherwise, downtime will begin between the "start" and "end" times and last for "duration" seconds. The "start" and "end" arguments are specified in time_t format (seconds since the UNIX epoch). The specified host downtime can be triggered by another downtime entry if the "trigger_id" is set to the ID of another scheduled downtime entry. Set the "trigger_id" argument to zero (0) if the downtime for the specified host should not be triggered by another downtime entry.

Removing downtimes with a shell command

All downtimes related to a host, including all its services, can be removed as follows. Note that the host variable is the name reported by hostname (not the FQDN returned with --fqdn). For example: cp4021.

echo -n "[$(date +'%s')] DEL_DOWNTIME_BY_HOST_NAME;$host" > /var/lib/icinga/rw/icinga.cmd

Disabling notifications programmatically

There many scenarios in which we may want a role to run its puppet logic to fully or partially provision its configuration, but not create alerts. Examples of this are:

  • Hosts in the process of being installed, set up and not yet servicing real traffic (but need to run puppet before they are 100% ready)
  • Decommissioned hosts
  • hosts with hardware problems for an extended period of time, and for which manual downtime would be inappropiate.
  • Canary hosts (like cp1008 aka pink unicorn)
  • Spare systems that are running but are not really doing anything (aka spare::system role)

For discussions about this topic, see task T151632

To disable notifications on a host, set profile::base::notifications on hiera to disabled (it defaults to enabled). This is intended as a temporary (even if extended on time) measure- if no check should exist when the server is in full production, just do not add it in the first place or change its LEVEL.

Failover Icinga between the active and passive servers

[As of Jan. 2018] Icinga is currently installed in an active/passive configuration on icinga1001.wikimedia.org (eqiad, usually active) and icinga2001.wikimedia.org (codfw, usually passive). Use icinga.wikimedia.org to check which one is the active one at any given time with: dig +short icinga.wikimedia.org.

To failover between the two servers, follow these steps:

  • Prepare a Puppet patch similar to https://gerrit.wikimedia.org/r/c/operations/puppet/+/489791
  • Prepare a DNS patch similar to https://gerrit.wikimedia.org/r/c/operations/dns/+/489777 Confirm the TTL is low (5M) to allow for quick reverting if needed.
  • If a new server name, double check that the email sender address is whitelisted in the AQL portal. That is the Mail2SMS service we use to turn email notifications into pages. Find the credentials in the "aql" file in pwstore.
  • Announce the failover on IRC with some advance, and plan to avoid SWAT, Puppet SWAT and other ongoing maintenances or outages. Also avoid the time of the root's crontab on the passive host to sync Icinga state files (currently at minute 33 of each hour).
  • Check that on the passive host the NSCA process doesn't have a tremendous number of subprocesses, as a precaution stop it, verify that all child processes were killed (or proceed to killall them) and start it again.
  • Log on #wikimedia-operations the start of the failover
  • Disable Puppet on both hosts: sudo cumin 'A:icinga' "disable-puppet 'Failover Icinga - $USER'"
  • Merge, submit and puppet-merge the Puppet patch
  • Enable and run Puppet on the previously active server to make it passive, check for errors: sudo run-puppet-agent -e "Failover Icinga - $USER"
  • On the previously passive server, run the script to sync Icinga state files: sudo sync_icinga_state
  • Merge and submit the DNS patch and deploy the change, see DNS#authdns-update or ask in #wikimedia-traffic
  • On the previously passive server, ensure that the DNS is updated, if not wait for the TTL to expire: dig +short icinga.wikimedia.org
  • Enable and run Puppet on the previously passive server to make it active, check for errors: sudo run-puppet-agent -e "Failover Icinga - $USER"
  • Check that https://icinga.wikimedia.org/icinga/ is running properly. If you see a red message "Notifications are disabled", your browser is most likely still pointing to the old active server. Flush the DNS cache or wait the TTL to expire.
  • Log on #wikimedia-operations the end of the failover

Check validity of the Icinga's config

sudo /usr/sbin/icinga -v /etc/icinga/icinga.cfg

Meta-monitoring of Icinga itself

We're currently externally monitoring Icinga with a custom script. For the details see Wikitech-static#Meta-monitoring.

Restarting

To avoid alerts from external meta-monitoring, meta-monitoring should be disabled on Wikitech-static before restarting normally with systemctl. Details on how to disable meta-monitoring can be found here: Service_restarts#Icinga

IRC bot

How to add some but not all notifications to a specific IRC channel.

The class used is profile::icinga::ircbot which uses ::ircecho and is included in profile::icinga. Server, nickname and port are configured in Hiera in hieradata/role/common/alerting_host.yaml. The tcpircbot class is unrelated though also included on the Icinga server.

  • Create 2 custom notification commands (modules/nagios_common/templates/notification_commands.cfg.erb), notify-service-by-irc-dcops and notify-host-by-irc-<YOUR CHANNEL>. So one for services and one for hosts. Copy the commandline from existing "by-irc" commands but make sure the output gets appended to a new log file, /irc-<YOUR CHANNEL>.log
  • Create a new Icinga contact (private repo, modules/secret/secrets/nagios/contacts.cfg), irc-<YOUR CHANNEL>. Copy an existing "irc-" contact but adjust host_notification_command and service_notification_command to use your new commands (and logfile).
  • Create a new Icinga contactgroup (public repo, modules/nagios_common/files/contactgroups.cfg) for datacenter ops and add the special contact you created to it (and optional the human members of your group so they get notified too). Check Icinga config is ok after running puppet (icinga -v /etc/icinga/icinga.cfg)
  • In puppet identify the monitoring::service / nrpe::monitor_service classes that should notify to to this channel (or make new ones) and add the new contactgroup as a parameter to them.
  • On the Icinga server go to /var/log/icinga/ and check if the new logfile has been created (you may have to touch it manually the very first time) and alerts get logged to it
  • Configure ircecho (modules/profile/manifests/icinga/ircbot.pp) to map the logfile to your IRC channel ($ircecho_logs, see existing examples) (restart ircecho?)

Avoid Icinga spam on new server installs

< volans> if you have more of those to do my suggestion is to temporarily disable puppet on icinga
< volans> downtime for 1h, then merge the puppet patch, either wait 30 min or force a run on the new hosts (*not* all together though, -b 15 is a good one), then re-enable puppet on 
                icinga and run the downtime with the force-puppet-run
< volans> the double downtime is because the puppet apply might take down things that were already checked
< volans> so you want to downtime the existing checks and then the new ones later on
< volans> if you re-enable puppet late enough you don't need the downtime as all should already be green at the first attempt

The above translates to:

  1. disable puppet on icinga: ex: [icinga1001:~] $ sudo puppet agent --disable <reason/ticket ID>
  2. downtime for 1h: ex: dzahn@cumin1001:~$ sudo cookbook sre.hosts.downtime -r new_install -t T236437 -H 1 mw13[63,74-83].eqiad.wmnet
  3. merge in Gerrit / puppet-merge on puppetmaster
  4. force puppet run: ex: dzahn@cumin1001:~$ sudo -i cumin -b 15 'mw13[63,74-83].eqiad.wmnet' 'run-puppet-agent -q'
  5. re-enable puppet on icinga: [icinga1001:~] $ sudo puppet agent --enable
  6. run downtime with force-puppet-run: ex: dzahn@cumin1001:~$ sudo cookbook sre.hosts.downtime -r new_install -t T236437 -H 1 --force-puppet mw13[63,74-83].eqiad.wmnet

How to handle active alerts

Concepts

The three numbers signify, from left to right, Unacknowledged, Acknowledged, and Handled.
Icinga provides tooltips to remind what each number signifies.

Icinga has a concept of handled vs. unhandled alerts. Handled alerts means they are either in a scheduled downtime or have been acknowledged as "known".

Unhandled alerts are the ones that are not known yet and need attention.

When looking at the Icinga web UI the ones we should pay special attention to are the ones that are both "unhandled" and in status "CRITICAL".

In the images below you can see 3 numbers each in the red sections. One section is about hosts and the other about services on hosts. The first of the 3 numbers is the number of unhandled CRITs.

Our goal is to keep the number of CRITICALs low and reasonable, in a way that balances the "good knowledge of unhandled ongoing issues" and "spam alerting" (making it more difficult to detect problems). Ongoing problems that are already in progress of being fixed should be turned into handled ("known") alerts.


You can also go directly to the URL below to see all unhandled alerts at once, besides CRITs this also includes WARNs and UNKNOWNS:

Merely disabling notifications does not move alerts out of the unhandled section and has the potential to be forgotten. Consider using downtimes and ACKs instead. ACKs automatically are removed on the next state change. IMPORTANT: Never ack/disable an alarm blindly (check with owner or research yourself).

Statements

Lines on /alerts mean "there is something bad happening" and nobody saw it yet, as they're both unACKed and unDOWNTIMEd.

A perfect /alerts page is an empty /alerts page.

All alerts can be early signs of a larger failure, potentially user facing down the road (if not already).

SREs monitoring that page are from all backgrounds and can't know about the real severity of every alert.

UNKNOWN are as bad as CRITICALs as they can be hiding a CRITICAL.

WARNINGs are a bit hard to sort out, but could become CRITICALs.

Hosts and services must be downtimed before any maintenance. (Either via the UI or via cookbook)

All SREs should monitor for alerts on /alerts or #wikimedia-operations.

Runbook

  • ACK resourceloader-alerts (with T203485)
  • CRITICALs
    • Look for a relevant open task (eg. by the hostname). If none, open a task
    • Check the service note, if not helpful, ask for it to be updated in the task
    • If any, add troubleshooting to the task
    • If confident enough to fix the issue, fix it. If not leave it to the service owner.
    • If any risk of the issue getting worse (or in doubt) ask about it on IRC, ping relevant teams. Rule of thumb: if active for more than 24h it's probably not needed
    • If you are owner of the service or are handling it, ack alert with relevant task. Otherwise, leave it ongoing with a note pointing to the task you just opened
  • UNKNOWN
    • Treat as CRITICAL
  • WARNING
    • Ignore everything with duration < 24/48h (transient). Give enough time for owners to notice (e.g. is he/she on vacation? Timezone?).
    • If domain specific (e.g. Databases) ask on the relevant IRC channel/preferred mechanism (e.g. #wikimedia-data-persistence). Avoid if possible single person pinging (but due to SPOF, that may be still needed).
    • Everything else, treat as CRITICALs (but more relax)

If you're thinking "this alert should open a task automatically" mention it on T225140

If you believe a team is not handling alerts for things you believe they own, or a single service is creating too much spam alert, bring this up on through an awareness communication channel (e.g. SRE meetings, a manager) to try to give visibility as to why that may be happening and try to get it fixed.