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1 Don't reboot, debug! A medic first aid course in debugging your server Joshua Thijssen @JayTaph

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2 Joshua Thijssen Consultant and trainer Author of the Symfony Rainbow Series http://www.symfony-rainbow.com Blog: http://adayinthelifeof.nl Email: jthijssen@noxlogic.nl Twitter: @jaytaph Tech nalyze WWW.TECHANALYZE.IO

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3 It's not

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3 It is It's not

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4 Our website is not working anymore!!!

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Have you tried turning it off and on again? 5

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6 Manager Not a suit

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6 Fix it! Every minute we’re losing money! Manager Not a suit

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8 Deal now or deal later?

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9

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9 ➡ Is it reproducible later? Probably not.

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9 ➡ Is it reproducible later? Probably not. ➡ Are you solving the problem, or desperately trying to remove a symptom?

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9 ➡ Is it reproducible later? Probably not. ➡ Are you solving the problem, or desperately trying to remove a symptom? ➡ Short term relieve vs long term solution

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10

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➡ Actually analyze, maybe fix the problem. 10

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➡ Actually analyze, maybe fix the problem. ➡ It will cost less to analyze/fix it now, than to fix it later. 10

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➡ Actually analyze, maybe fix the problem. ➡ It will cost less to analyze/fix it now, than to fix it later. 10

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12

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12 ➡ We reboot our system every night!

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12 ➡ We reboot our system every night! ➡ Why? Memory leaks? Just crappy code?

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12 ➡ We reboot our system every night! ➡ Why? Memory leaks? Just crappy code? ➡ There is some state not handled correctly!

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12 ➡ We reboot our system every night! ➡ Why? Memory leaks? Just crappy code? ➡ There is some state not handled correctly! ➡ What happens when # users increase with 200%? Restart every 12 hours?

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12 ➡ We reboot our system every night! ➡ Why? Memory leaks? Just crappy code? ➡ There is some state not handled correctly! ➡ What happens when # users increase with 200%? Restart every 12 hours? ➡ Let’s hope you won’t get many visitors!

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Find the culprit 13

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Bottleneck Troubleshooting Flowchart (BTF) 14

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Site is slow or not responding. It’s your DB Bottleneck Troubleshooting Flowchart (BTF) 14

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15

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➡ Apache / PHP 15

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➡ Apache / PHP ➡ Monitoring / backup 15

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➡ Apache / PHP ➡ Monitoring / backup ➡ Hanging cron jobs & runaway tools 15

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➡ Apache / PHP ➡ Monitoring / backup ➡ Hanging cron jobs & runaway tools ➡ Connectivity / DNS problems 15

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16 Linux 101

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17 Processes

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18

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18 ➡ Isolated userspace.

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18 ➡ Isolated userspace. ➡ PID (process id) and state.

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18 ➡ Isolated userspace. ➡ PID (process id) and state. ➡ Kernel “preempts”, or process yields.

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18 ➡ Isolated userspace. ➡ PID (process id) and state. ➡ Kernel “preempts”, or process yields. ➡ Multitasking.

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19

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20

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20 ➡ R Running or runnable

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20 ➡ R Running or runnable ➡ S Interruptible sleep

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20 ➡ R Running or runnable ➡ S Interruptible sleep ➡ D Uninterruptible sleep

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20 ➡ R Running or runnable ➡ S Interruptible sleep ➡ D Uninterruptible sleep ➡ T Stopped

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20 ➡ R Running or runnable ➡ S Interruptible sleep ➡ D Uninterruptible sleep ➡ T Stopped ➡ Z Defunct process (zombies)

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21

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21 ➡ Most processes are sleeping.

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21 ➡ Most processes are sleeping. ➡ External processes (and the kernel) can “wake up” a process at any time by sending “signals”.

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21 ➡ Most processes are sleeping. ➡ External processes (and the kernel) can “wake up” a process at any time by sending “signals”. ➡ Fire signals with “kill”.

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22

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22 ➡ Uninterruptible means it won’t handle signals (directly), but waits on its task to finish (it must wake up by itself).

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22 ➡ Uninterruptible means it won’t handle signals (directly), but waits on its task to finish (it must wake up by itself). ➡ Used for high-performance loops that needs to focus (like I/O).

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22 ➡ Uninterruptible means it won’t handle signals (directly), but waits on its task to finish (it must wake up by itself). ➡ Used for high-performance loops that needs to focus (like I/O). ➡ Still can be preempted by the scheduler!

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23

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23 ➡ Zombies aren’t bad.

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23 ➡ Zombies aren’t bad. ➡ It’s just bad programming or administration that creates zombies.

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23 ➡ Zombies aren’t bad. ➡ It’s just bad programming or administration that creates zombies. ➡ They will not eat brains (at least not much).

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23 ➡ Zombies aren’t bad. ➡ It’s just bad programming or administration that creates zombies. ➡ They will not eat brains (at least not much). ➡ But there shouldn’t be many.

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24 Load average

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25

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25 ➡ 1 minute, 5 minutes, 15 minutes averages

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25 ➡ 1 minute, 5 minutes, 15 minutes averages ➡ Calculated as the number of runnable processes.

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25 ➡ 1 minute, 5 minutes, 15 minutes averages ➡ Calculated as the number of runnable processes. ➡ Depends on number of CPU’s!

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26 14:57:22 up 35 days, 18:57, 1 user, load average: 1.52, 0.66, 0.27

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26 14:57:22 up 35 days, 18:57, 1 user, load average: 1.52, 0.66, 0.27 ➡ 1.52 average runnable (or blocking) processes in the last minute.

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26 14:57:22 up 35 days, 18:57, 1 user, load average: 1.52, 0.66, 0.27 ➡ 1.52 average runnable (or blocking) processes in the last minute. ➡ 0.66 average in 5 minutes

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26 14:57:22 up 35 days, 18:57, 1 user, load average: 1.52, 0.66, 0.27 ➡ 1.52 average runnable (or blocking) processes in the last minute. ➡ 0.66 average in 5 minutes ➡ 0.27 average in 15 minutes.

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26 14:57:22 up 35 days, 18:57, 1 user, load average: 1.52, 0.66, 0.27 ➡ 1.52 average runnable (or blocking) processes in the last minute. ➡ 0.66 average in 5 minutes ➡ 0.27 average in 15 minutes. ➡ Single CPU: 52% more than it can handle.

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26 14:57:22 up 35 days, 18:57, 1 user, load average: 1.52, 0.66, 0.27 ➡ 1.52 average runnable (or blocking) processes in the last minute. ➡ 0.66 average in 5 minutes ➡ 0.27 average in 15 minutes. ➡ Single CPU: 52% more than it can handle. ➡ quad core system: not doing very much

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27 Memory

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28 Q: How much memory does this process use? This is REALLY hard question to answer! It depends on many factors!

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29 ➡ Virtual memory ➡ Shared memory ➡ Resident memory ➡ Swapped memory

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30

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30 ➡ 4GB memory space, even if you have less memory installed.

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30 ➡ 4GB memory space, even if you have less memory installed. ➡ 1GB is reserved for kernel.

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30 ➡ 4GB memory space, even if you have less memory installed. ➡ 1GB is reserved for kernel. ➡ Kernel can swap out memory.

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30 ➡ 4GB memory space, even if you have less memory installed. ➡ 1GB is reserved for kernel. ➡ Kernel can swap out memory. ➡ CPU pagefaults and loads back pages.

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31

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31 ➡ Process can allocate memory, but does not necessary use it (for instance: preallocation)

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31 ➡ Process can allocate memory, but does not necessary use it (for instance: preallocation) ➡ VIRT will increase!

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32

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33 Q: How much free memory does this system have? This is an easier, but still hard question to answer!

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34 $ free -m total used free shared buffers cached Mem: 375 349 25 0 111 94 -/+ buffers/cache: 143 231 Swap: 400 7 392

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35 Monitoring

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36 ➡ Monitor everything ➡ System / infra monitoring ➡ Application monitoring

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39 Logging Logging

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40 ➡ Log EVERYTHING from all sources. ➡ Filter later.

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41 $ php composer.phar require monolog/monolog ➡ syslog ➡ files ➡ mail ➡ slack / hipchat / irc ➡ logstash

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42 System tools

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TAIL 43

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44

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44 ➡ Most daemons will log into /var/log/*

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44 ➡ Most daemons will log into /var/log/* ➡ tail -f /var/log/messages

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44 ➡ Most daemons will log into /var/log/* ➡ tail -f /var/log/messages ➡ Many times, this is ALL you need!

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45

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45 ➡ Know your tools (top, htop, vmstat, iostat, ps)

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45 ➡ Know your tools (top, htop, vmstat, iostat, ps) ➡ Know the /proc filesystem

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45 ➡ Know your tools (top, htop, vmstat, iostat, ps) ➡ Know the /proc filesystem ➡ sniff around with tcpdump, netstat, nc etc...

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45 ➡ Know your tools (top, htop, vmstat, iostat, ps) ➡ Know the /proc filesystem ➡ sniff around with tcpdump, netstat, nc etc... ➡ man

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46 strace

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47 ➡ strace displays system calls and signals ➡ Communication between applications and the kernel.

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48 $ strace -ff -p .... socket(PF_INET, SOCK_STREAM, IPPROTO_TCP) = 20 fcntl(20, F_GETFL) = 0x2 (flags O_RDWR) fcntl(20, F_SETFL, O_RDWR|O_NONBLOCK) = 0 connect(20, {sa_family=AF_INET, sin_port=htons(11211), sin_addr=inet_addr("127.0.0.1")}, 16) = -1 EINPROGRESS (Operation now in progress) poll([{fd=20, events=POLLOUT}], 1, -1) = 1 ([{fd=20, revents=POLLOUT}]) write(20, "get ez_client1/acls/"..., 44) = 44 read(20, "END\r\n", 8196) = 5 write(20, "get ez_client1/acl/g"..., 40) = 40 read(20, "END\r\n", 8196) = 5 write(20, "quit\r\n", 6) = 6 shutdown(20, 2 /* send and receive */) = 0 close(20) = 0 mkdir("/tmp/smarty", 0777) = -1 EEXIST (File exists) chmod("/tmp/smarty", 0777) = 0 mkdir("/tmp/smarty", 0777) = -1 EEXIST (File exists) chmod("/tmp/smarty", 0777) = 0 access("/userdata/client1/user/templates/nl/block-right-last.tpl", F_OK) = -1 ENOENT (No such file or directory) access("/userdata/client1/user/templates/block-right-last.tpl", F_OK) = -1 ENOENT (No such file or directory) access("/userdata/client1/theme/templates/nl/block-right-last.tpl", F_OK) = -1 ENOENT (No such file or directory) access("/userdata/client1/theme/templates/block-right-last.tpl", F_OK) = -1 ENOENT (No such file or directory) access("/etc/noxlogic/root/themes/ezshopping/templates/nl/block-right-last.tpl", F_OK) = -1 ENOENT (No such file or directory) access("/etc/noxlogic/root/themes/ezshopping/templates/block-right-last.tpl", F_OK) = -1 ENOENT (No such file or directory) mkdir("/tmp/smarty", 0777) = -1 EEXIST (File exists) chmod("/tmp/smarty", 0777) = 0 access("/userdata/client1/user/templates/nl/block-right.tpl", F_OK) = -1 ENOENT (No such file or directory) access("/userdata/client1/user/templates/block-right.tpl", F_OK) = -1 ENOENT (No such file or directory) access("/userdata/client1/theme/templates/nl/block-right.tpl", F_OK) = -1 ENOENT (No such file or directory) access("/userdata/client1/theme/templates/block-right.tpl", F_OK) = -1 ENOENT (No such file or directory) access("/etc/noxlogic/root/themes/ezshopping/templates/nl/block-right.tpl", F_OK) = -1 ENOENT (No such file or directory) access("/etc/noxlogic/root/themes/ezshopping/templates/block-right.tpl", F_OK) = -1 ENOENT (No such file or directory) mkdir("/tmp/smarty", 0777) = -1 EEXIST (File exists)

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49 $ strace ping www.google.com .... mprotect(0xb757f000, 4096, PROT_READ) = 0 munmap(0xb76d8000, 44104) = 0 stat64("/etc/resolv.conf", {st_mode=S_IFREG|0644, st_size=59, ...}) = 0 socket(PF_INET, SOCK_DGRAM|SOCK_NONBLOCK, IPPROTO_IP) = 3 connect(3, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr("192.168.178.4")}, 16) = 0 gettimeofday({1347446161, 382120}, NULL) = 0 poll([{fd=3, events=POLLOUT}], 1, 0) = 1 ([{fd=3, revents=POLLOUT}]) send(3, "u\205\1\0\0\1\0\0\0\0\0\0\3www\6google\3com\0\0\1\0\1", 32, MSG_NOSIGNAL) = 32 poll([{fd=3, events=POLLIN}], 1, 5000

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➡ strace -e trace=open ➡ strace -ff -p 50

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51 vmstat

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52 $ vmstat 1 procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu---- r b swpd free buff cache si so bi bo in cs us sy id wa 0 0 896 17208 124784 121964 0 0 0 0 73 159 0 1 99 0 2 0 896 14968 125628 121976 0 0 844 0 6857 29935 5 58 35 2 2 0 896 14472 125628 121964 0 0 0 0 10691 48526 10 90 0 0 2 0 896 13976 126120 121952 0 0 476 252 10430 49144 7 91 0 2 0 0 896 12744 127016 121968 0 0 896 0 7799 38732 3 71 23 3 0 0 896 12744 127016 121964 0 0 0 0 30 93 0 0 100 0 0 0 896 12760 127016 121964 0 0 0 0 30 92 0 0 100 0 0 0 896 12760 127016 121964 0 0 0 0 29 99 0 1 99 0 0 0 896 12760 127016 121964 0 0 0 0 32 110 0 0 100 0 0 0 896 12752 127024 121964 0 0 0 324 33 108 0 0 99 1 0 0 896 12752 127024 121964 0 0 0 0 30 103 0 0 100 0 0 0 896 12752 127032 121964 0 0 0 12 34 108 0 0 100 0 0 0 896 12752 127032 121964 0 0 0 0 30 105 0 0 100 0 0 0 896 12752 127032 121964 0 0 0 236 80 101 0 1 99 0

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53 System tap / dtrace System TAP (dtrace)

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54 ➡ Unobtrusive probes inside the kernel ➡ Scripts written in D language. ➡ SUN / Solaris only (licensing)

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55 ➡ “GPL” version of dtrace ➡ Awesome, but complex ➡ But you need / want debug info packages

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probe syscall.open { printf(“%s(%d) open (%s)\n”, execname(), pid(), argstr); } 56 stap syscall.stp

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57 ➡ There are some “providers” in the PHP core (zend_dtrace.{c,h,d})

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58 ➡ Valgrind ➡ GDB ➡ XDebug / profiler ➡ MySQL proxy

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59 Think about your app / infra BEFORE going live...

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Make a plan 60

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61

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61 ➡ Design for (vertical) scalability.

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61 ➡ Design for (vertical) scalability. ➡ Remove SPOFs.

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61 ➡ Design for (vertical) scalability. ➡ Remove SPOFs. ➡ Horizontal scalability is easier, but more restrictive.

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61 ➡ Design for (vertical) scalability. ➡ Remove SPOFs. ➡ Horizontal scalability is easier, but more restrictive. ➡ Configuration is key.

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61 ➡ Design for (vertical) scalability. ➡ Remove SPOFs. ➡ Horizontal scalability is easier, but more restrictive. ➡ Configuration is key. ➡ Don’t run on full capacity. Have a contingency buffer for peaks and know how to scale out

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62

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62 ➡ One machine for one purpose (app / mail / cron / db / etc).

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62 ➡ One machine for one purpose (app / mail / cron / db / etc). ➡ Virtual machines are easy to setup and maintain (puppet / ansible) and are cheap.

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62 ➡ One machine for one purpose (app / mail / cron / db / etc). ➡ Virtual machines are easy to setup and maintain (puppet / ansible) and are cheap. ➡ Try to async as much as possible.

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62 ➡ One machine for one purpose (app / mail / cron / db / etc). ➡ Virtual machines are easy to setup and maintain (puppet / ansible) and are cheap. ➡ Try to async as much as possible. ➡ Message queues are easy to implement (gearman / *MQ etc).

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63 Recap Conclusion

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64

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65 ➡ Don’t reboot, debug!

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65 ➡ Don’t reboot, debug! ➡ Analyze what’s going on,

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65 ➡ Don’t reboot, debug! ➡ Analyze what’s going on, ➡ find and isolate the culprit.

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65 ➡ Don’t reboot, debug! ➡ Analyze what’s going on, ➡ find and isolate the culprit. ➡ Threat the problem, not the symptoms.

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66

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66 ➡ There are many tools out there to analyze your system realtime.

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66 ➡ There are many tools out there to analyze your system realtime. ➡ Know your running environment (even it’s “not your business”).

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66 ➡ There are many tools out there to analyze your system realtime. ➡ Know your running environment (even it’s “not your business”). ➡ Ask 3rd party help if needed.

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67

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Find me on twitter: @jaytaph Find me for development and training: www.noxlogic.nl Find me on email: jthijssen@noxlogic.nl Find me for blogs: www.adayinthelifeof.nl Thank You! https://joind.in/14205