Q: discoveryd process uses 100% CPU - Safari Can't find the server

I've been having the same problem since Yosemite installed.  I'm generally not using Safari, but Firefox or Chrome.  I know that Chrome  does have some backend processes that can run when the browser is closed, MightyText and PrinterShare are two android apps that use that mechanism, I believe.  I do know that it will happen (that is the launchd CPU % will grow to 100%) over time.  I had thought, before reading this thread, that some setting was off on my router, since not only is my Mac affected, but my entire network looses connection to the internet (via Comcast cable modem) when this happens.  What has been odd is the lack of any error messages in the router.  I run a TP-Link TL-WDR4300, but running ww-drt firmware (latest compatible).  Sometimes I can reboot the router and the problem will clear, sometimes not.  My usual parallel routine, but on the cable modem does not resolve my connectivity.  In order of chance of success for a temporary reprieve from internet exile, these things seem to work best, in this order (relative, not absolute, and none 100% of the time):

1) Rebooting the Mac - this will reset the CPU use and the problem will resolve maybe 50% of  the time.

2) Rebooting the Router - this will resolve the problem, but usually only for a short time, maybe 20% of the time

3) insuring only one network connection is enabled, using built-in "helpers" to test or configure network connections, alternately turning on all 3 direct to router connections (2 physical and 1 wifi MacPro old style) - keeps me busy but only 5% chance of resolving at best.  When it's worked, my impression is that "assist me" then "assistant" in Network Preferences has at times resolved the connectivity issue, but it could be just coincidence,

4) Rebooting the Comcast Modem 0% effective, but what I had to do in the past to resolve loss of Comcast network)  Also know telling issues in the event log of the modem, I just see the steps it goes through when rebooting, nothing before or after unusual.

5) Messing with the wwdrt settings (various) 0% effective

Side notes that may or may not be germain or important:  Once I noticed the discoveryd process increasing use to 100%, I always have killed that first before attempting to resolve.  While that alone, as far as I can tell, never resolved the connectivity issue for me .  I was granted the insight to look at the Activity Monitor after experiencing the problem updating iTunes to the latest version, which would attempt with or without my prompting countless times without success.  The
App Store could not make it happen and I tried everything I could think of.  Another person with that problem (iTunes 12.0 to 12.0.1 update fails, but reports as successful on App Store, while remaining listed as "need to install") eventually was advised to uninstall iTunes (not the intuitive and enjoyable content, the frustratingly complex and buggy app), and I had to do so as well, resolving the issue.  But when this was happening the App Store was highlighted in Red in activity monitor, presumably due to the inability to install the iTunes update.  I don't know what effect this could have on calls out to DNS or other network traffic. 

I had wanted to attempt a DNS flush command to see if that would help, since I remember years ago experiencing a problem that behaved like this on Windows (likely Win XP prior to SP 2), which quickly resolved when DNS flush forced by PC.  But I don't recall any symptom including a process hogging CPU in conjunction, just an otherwise unfixable inability to get out of the LAN to the internet.  I think, as it turns out, Windows Network Sharing was implicated and finally fixed.  For what it's worth, through a very fuzzy memory lens.

Any confirmed fixes or helpful workarounds that have been tested a bit by someone smarter than me (I see thousands of candidates with their hands up!) will be happily implemented, or attempted on my machine with commitment to followup with results.  BTW, srobert thank you and for your continued focus and willingness continue to beta test.  How do we get him promoted to level 2, and does that help in court or when dealing with the IRS?  I'm kidding, but the total of the work done by everyone contributing just to this one thread (except this post) is really encouraging and helpful and I think we can't say that to you smart  persons enough.  Why it's needed, well, that would require a really boring set of stories that hopefully will skip a generation and be told to your grandchildren.   A lot of people think we should still be in Vietnam, that Nixon was not any worse than President fillintheblank, and that Fox News presents information not adapted to fit their ideological agenda.  Of course, these aren't all the same people, but I'll leave the ven diagrams to your imagination.   One more, sorry, truth roll very boring and probably sounds smug, but Reagan was (one of) our best President(s), ever.  That is very likely, not very close to the truth.

On my home network I have two Macs: a 2013 MacBook Air and an 2008 MacPro.  There are also usually a couple of iPhones and two iPads.  There are also numerous non-computing devices.

The MacBook Air works perfectly.  The iPads work perfectly.  The iPhones seem to have intermittent doses of the discoveryd problem: good network connection  but unable to find anything.  Turning WiFi off and using the cellular network gets rid of the problem.

The MacPro has the discoveryd issue bad.  Unlike most of the reports here it manifests when the computer is started up from cold. On most cold starts discoveryd will go to 100% CPU and no DNS lookups work for between 15 and 20 minutes.  Then discoveryd starts working.  Most days it keeps working all day but occasionally it will go bad during the day for a few minutes and then clear up.

I just thought it was worth reporting the variation on the theme.  It seems this thing is a dog with fleas.

To all:

Interesting read on Ars - seems like the problem is discoveryd which replaced mDNSResponder in 10.10.  Here is the article. Looks like you can replace with mDNSReposnder if you are brave or wait for Apple to fix discoveryd.

Add another victim to the discoveryd problem.  I have even installed the 10.10.2 beta hoping for fix to no avail.

Add me too.

Same problem here at my Mac mini (Yosemite 10.10.1):

99% CPU load for discovery process and constantly growing memory consumption up to several GB

Solution: Uncheck "dynamical global hostname" at System - Sharing - Devicename and use local device name (e.g. mysupermac.local)

It might solve your problem but there are other issues : on my mac, the "dynamical global hostname" was not checked but I have the issue, and still have it. I guess several programs or situation are causing discoveryd to go crazy

Dynamic global hostname was not checked on my computer either.  Still looking and hoping for a fix.  I'm even running 10.10.2 beta.  I've pretty much had to stop using my desktop iMac.

The link in cwilmo's post of 2015 01/13 is bad. The correct link is:

http://arstechnica.com/apple/2015/01/why-dns-in-os-x-10-10-is-broken-and-what-yo u-can-do-to-fix-it/

(With the colons and slashes changed to "deactivate" it, the incorrect hidden link was to http <colon> <slash> <slash> http <slash slash> arstechnica.com/apple/2015/01/why-dns-in-os-x-10-10-is-broken-and-what-you-can- do-to-fix-it/)

I haven't read the linked article yet myself so can't comment on it.

This just started happening to me. Im trying to update Flash, it hangs on the download at 25% and I notice that discoverd starts to use over 100% CPU.

What is discoveryd?  Should I cotinue to block its access?

I am running Yosemite 10.10.1 so there should not be a problem- but I am still having to block discoveryd oin the Norton Firewall until I get a definitive answer on whether discoveryd attempted connects from IP 224.0.0.251 and ff02::fb are valid.

I did something that seems to have "solved" the problem for now. I redirected all incoming DNS calls (ports 53) to my routers IP address using my routers port forwarding feature. I figure I could just let the router bounce the activity back. After doing that I am no longer getting flooded by DNS requests and my discoveryd activity is back to normal.

ok so i just plugged in my ethernet cord and the issue went away. Thankyou Lord lol.  We'll see how long this lasts if it comes back you all will here from me....      Aside from pluggin in my ethernet cable for a few seconds i also turned off file sharing and did the terminal deal that someone posted and entered my password.  I'm about to restart my CPU just to make sure things are in tact.  I'm exstatict right now.  my computer was overheating and everything.  I even purchased a new battery.  The old one was done regardless it was that time lol.  So here we go i'm gonna run Logic X and hope for the best.  Thanks everyone for your posts helped me trouble shoot seems the discoveryd is a wireless network issue. 

wireless works fine also.... before doing this i had an "!" in my wireless icon also