{"action":"created","comment":{"url":"https://api.github.com/repos/cryptic-io/cryptic-chat/pulls/comments/26432230","id":26432230,"diff_hunk":"@@ -0,0 +1,166 @@\n+---\n+layout: post\n+title: Rabbit Hole\n+tags: debug php sysdig dns\n+username: mediocregopher\n+---\n+\n+# Rabbit Hole\n+\n+We've begun rolling out [SkyDNS][skydns] at my job, which has been pretty neat.\n+We're basing a couple future projects around being able to use it, and it's made\n+dynamic configuration and service discovery nice and easy.\n+\n+This post chronicles catching a bug because of our switch to SkyDNS, and how we\n+discover its root cause. I like to call these kinds of bugs \"rabbit holes\"; they\n+look shallow at first, but anytime you make a little progress forward a little\n+more is always required, until you discover the ending somewhere totally\n+unrelated to the start.\n+\n+## The Bug\n+\n+We are seeing *tons* of these in the SkyDNS log:\n+\n+```\n+[skydns] Feb 20 17:21:15.168 INFO      | no nameservers defined or name too short, can not forward\n+```\n+\n+I fire up tcpdump to see if I can see anything interesting, and sure enough run\n+across a bunch of these:\n+\n+```\n+# tcpdump -vvv -s 0 -l -n port 53\n+tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes\n+    ...\n+    $fen_ip.50257 > $skydns_ip.domain: [udp sum ok] 16218+ A? unknown. (25)\n+    $fen_ip.27372 > $skydns_ip.domain: [udp sum ok] 16218+ A? unknown. (25)\n+    $fen_ip.35634 > $skydns_ip.domain: [udp sum ok] 59227+ A? unknown. (25)\n+    $fen_ip.64363 > $skydns_ip.domain: [udp sum ok] 59227+ A? unknown. (25)\n+```\n+\n+It appears that some of our front end nodes (FENs) are making tons of DNS\n+requests trying to find the A record of `unknown`. This is not going to work;\n+something on our FENs is doing something insane and is breaking.\n+\n+## The FENs\n+\n+Hopping over to my favorite FEN we're able to see the packets in question","path":"_posts/2015-3-11-rabbit-hole.md","position":47,"original_position":47,"commit_id":"0658b4b95207e7909407649f63c742a276ef88dd","original_commit_id":"0658b4b95207e7909407649f63c742a276ef88dd","user":{"login":"akenn","id":405000,"avatar_url":"https://avatars.githubusercontent.com/u/405000?v=3","gravatar_id":"","url":"https://api.github.com/users/akenn","html_url":"https://github.com/akenn","followers_url":"https://api.github.com/users/akenn/followers","following_url":"https://api.github.com/users/akenn/following{/other_user}","gists_url":"https://api.github.com/users/akenn/gists{/gist_id}","starred_url":"https://api.github.com/users/akenn/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/akenn/subscriptions","organizations_url":"https://api.github.com/users/akenn/orgs","repos_url":"https://api.github.com/users/akenn/repos","events_url":"https://api.github.com/users/akenn/events{/privacy}","received_events_url":"https://api.github.com/users/akenn/received_events","type":"User","site_admin":false},"body":"By favorite do you just mean a random FEN? If so I'd just say \"Hopping on to one of our FENs we're able to see\".","created_at":"2015-03-14T00:20:15Z","updated_at":"2015-03-14T00:20:15Z","html_url":"https://github.com/cryptic-io/cryptic-chat/pull/33#discussion_r26432230","pull_request_url":"https://api.github.com/repos/cryptic-io/cryptic-chat/pulls/33","_links":{"self":{"href":"https://api.github.com/repos/cryptic-io/cryptic-chat/pulls/comments/26432230"},"html":{"href":"https://github.com/cryptic-io/cryptic-chat/pull/33#discussion_r26432230"},"pull_request":{"href":"https://api.github.com/repos/cryptic-io/cryptic-chat/pulls/33"}}},"pull_request":{"url":"https://api.github.com/repos/cryptic-io/cryptic-chat/pulls/33","id":30990909,"html_url":"https://github.com/cryptic-io/cryptic-chat/pull/33","diff_url":"https://github.com/cryptic-io/cryptic-chat/pull/33.diff","patch_url":"https://github.com/cryptic-io/cryptic-chat/pull/33.patch","issue_url":"https://api.github.com/repos/cryptic-io/cryptic-chat/issues/33","number":33,"state":"open","locked":false,"title":"add rabbit hole post","user":{"login":"mediocregopher","id":933154,"avatar_url":"https://avatars.githubusercontent.com/u/933154?v=3","gravatar_id":"","url":"https://api.github.com/users/mediocregopher","html_url":"https://github.com/mediocregopher","followers_url":"https://api.github.com/users/mediocregopher/followers","following_url":"https://api.github.com/users/mediocregopher/following{/other_user}","gists_url":"https://api.github.com/users/mediocregopher/gists{/gist_id}","starred_url":"https://api.github.com/users/mediocregopher/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/mediocregopher/subscriptions","organizations_url":"https://api.github.com/users/mediocregopher/orgs","repos_url":"https://api.github.com/users/mediocregopher/repos","events_url":"https://api.github.com/users/mediocregopher/events{/privacy}","received_events_url":"https://api.github.com/users/mediocregopher/received_events","type":"User","site_admin":false},"body":"An engaging post about a rabbit looking to find his place in a big rabbit world. Join him as he finds danger, adventure, and maybe even a little love. A fun-loving post that the whole family will enjoy.\r\n\r\n(Actually it's about me debugging some 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