bash - Restart a bunch of servers, keeping only a few down during the restart -

-

consider following script:

for host in $(get-all-hosts)   (restart-server $host; wait-for-server-to-come-up $host) & done

as might guess, restart-server restarts server , command wait-for-server-to-come-up blocks until server (e.g., grep -m 1 'server up' <(tail -f /path/to/log)).

this script restarts servers simultaneously. i'm curious what's simplest way modify script stop after fixed number of servers, , wait 1 server come before proceeding next restart maximum of, say, 4 servers down @ given time. 1 way know of doing restart in chunks of 4 , wait on of pids in each chunk, i'm hoping it's not hard smarter.

some scratch work toward solution:

second try, using ideas dennis's link. ideal vanilla bash solution:

mkfifo mfifo exec 3<>mfifo echo >&3 echo >&3 echo >&3 host in $(get-all-hosts)   read   (restart-server $host; wait-for-server-to-come-up $host; echo >&3) & done <&3

my biggest remaining complaint solution assumes there isn't named queue called mfifo that's in use. other that, haven't seen problems, , works expected far can tell.

xargs has parallelism feature similar parallel:

echo $(get-all-hosts) | tr ' ' '\n' | xargs -p 4 -n 1 ./blocking-restart

..where blocking-restart expected take name of single server, restart , wait until it's finished. note tr puts each host on own line, xargs expects.


Comments

Post a Comment

Popular posts from this blog

c# - SVN Error : "svnadmin: E205000: Too many arguments" -

-
i trying reposotries using c# code process svncommand = null; var psi = new processstartinfo("svnadmin"); psi.redirectstandardoutput = true; psi.redirectstandarderror = true; psi.useshellexecute = false; psi.arguments= @"dump c:\repositories\myrepo > c:\temp\myrepodumpfile.dump"; using (svncommand = process.start(psi)) { var myoutput = svncommand.standardoutput; var myerror = svncommand.standarderror; debug.write("output :" + environment.newline + environment.newline + myoutput.readtoend() + environment.newline + "error :" + environment.newline + environment.newline + myerror.readtoend()); svncommand.close(); } when use dump command commandline svnadmin dump c:\repositories\myrepo > c:\temp\myrepodumpfile.dump it works fine when try ...
Read more

c++ - Using OpenSSL in a multi-threaded application -

-
i have been writing soap client application in c++ on ubuntu using openssl https transport , pthreads threading. have number of threads - 1 central data acquisition thread periodically gets worker threads make soap requests via shared mutex protected queues. reading documentation openssl found is openssl thread-safe? in openssl faq describes mechanisms required ensure thread safety when using openssl. implemented , works fine. the reason question conceptual difficulty really. thinking implementing same functionality application has already, instead of using threads, create 2 seperate applications : 1 worker thread (of multiple copies running) , main data acquisition thread. use tcp sockets communicate between 2 rather mutex protected queues. may bad idea not important - confusing me would have implement same functions required ensure openssl thread safety in second approach or not? my guess not have , treated independent (indeed surely must many applications use openssl) re...
Read more

All overlapping substrings matching a java regex -

-
is there api method returns (possibly overlapping) substrings match regular expression? for example, have text string: string t = 04/31 412-555-1235; , , have pattern: pattern p = new pattern("\\d\\d+"); matches strings of 2 or more characters. the matches are: 04, 31, 412, 555, 1235. how overlapping matches? i want code return: 04, 31, 41, 412, 12, 55, 555, 55, 12, 123, 1235, 23, 235, 35. theoretically should possible -- there obvious o(n^2) algorithm enumerates , checks substrings against pattern. edit rather enumerating substrings, safer use region(int start, int end) method in matcher . checking pattern against separate, extracted substring might change result of match (e.g. if there non-capturing group or word boundary check @ start/end of pattern). edit 2 actually, it's unclear whether region() expect zero-width matches. specification vague, , experiments yield disappointing results. for example: string line = "xx90xx"; strin...
Read more