Re: What is elegant way to do configuration on server app
On Fri, Mar 27, 2015 at 7:28 PM, Jerry OELoo oylje...@gmail.com wrote: Hi Grant: Why use SIGHUP, Does it has something to do with configure file modification? I don't get it. Thank you. Long tradition. I have no idea why that particular signal is used, but it's a well-known convention. In any case, it's certainly sensible to use a signal; it's an easy way for one process to notify another, without needing much overhead or anything. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
Re: What is elegant way to do configuration on server app
Hi Grant: Why use SIGHUP, Does it has something to do with configure file modification? I don't get it. Thank you. On Thu, Mar 26, 2015 at 11:49 PM, Grant Edwards invalid@invalid.invalid wrote: On 2015-03-26, Ben Finney ben+pyt...@benfinney.id.au wrote: Jerry OELoo oylje...@gmail.com writes: Currently, I can just think out that I put status into a configure file, and service schedule read this file and get status value, That sounds like a fine start. Some advice: * You may be tempted to make the configuration file executable (e.g. Python code). Resist that temptation; keep it *much* simpler, a non-executable data format. Python's standard library has the ‘configparser’ module URL:https://docs.python.org/3/library/configparser.html to parse and provide the values from a very common configuration file format. Use that unless you have a good reason not to. I second the recommendation for configparser for stuff of simple to moderate complexity. If it gets too complex for configparser, you may want to consider JSON, or for even more complex stuff just use plain Python code in your config file (this can be very powerful and expressive, but can also be diffucult to implement safely). * Your program can “poll” the configuration file to see whether it has changed. At startup, read the config file's modification timestamp URL:https://docs.python.org/3/library/os.html#os.stat_result.st_mtime. Make a part of your event loop (assuming your server runs an event loop) that wakes up every N seconds (e.g. every 60 seconds) and checkes the file's modification timestamp again; if it's newer, record that value for future comparisons, then re-read the file for its values. That sounds rather Windowsesque. The more-or-less standard way to do handle the situation on Unix is to reread the config file when you get a SIGHUP. -- Grant Edwards grant.b.edwardsYow! ONE LIFE TO LIVE for at ALL MY CHILDREN in ANOTHER gmail.comWORLD all THE DAYS OF OUR LIVES. -- https://mail.python.org/mailman/listinfo/python-list -- Rejoice,I Desire! -- https://mail.python.org/mailman/listinfo/python-list
Re: What is elegant way to do configuration on server app
Grant Edwards invalid@invalid.invalid: That sounds rather Windowsesque. The more-or-less standard way to do handle the situation on Unix is to reread the config file when you get a SIGHUP. That, indeed, is the classic Unix way. However, Linux has now moved to systemd: ExecReload= Commands to execute to trigger a configuration reload in the service. This argument takes multiple command lines, following the same scheme as described for ExecStart= above. Use of this setting is optional. Specifier and environment variable substitution is supported here following the same scheme as for ExecStart=. One additional, special environment variable is set: if known, $MAINPID is set to the main process of the daemon, and may be used for command lines like the following: /bin/kill -HUP $MAINPID Note however that reloading a daemon by sending a signal (as with the example line above) is usually not a good choice, because this is an asynchronous operation and hence not suitable to order reloads of multiple services against each other. It is strongly recommended to set ExecReload= to a command that not only triggers a configuration reload of the daemon, but also synchronously waits for it to complete. URL: http://www.freedesktop.org/software/systemd/ma n/systemd.service.html Marko -- https://mail.python.org/mailman/listinfo/python-list
Re: What is elegant way to do configuration on server app
On Sat, Mar 28, 2015 at 12:23 AM, Marko Rauhamaa ma...@pacujo.net wrote: Chris Angelico ros...@gmail.com: The number of cases where this matters is fairly low. Doing the reload asynchronously is generally sufficient. Not sure. Not sure at all. Issues like this occupy a great part of my office hours. Only because your office hours are occupied by problems, not by the cases that work flawlessly. You don't see the innumerable times that fire-and-forget works fine :) And even if you have something that waits for the reload to finish, you'll usually fire-and-forget that command anyway. The command systemctl reload xyz.service is supposed to return when the service is happily running with the updated its configuration. Any failures should be reported with a nonzero exit code from systemctl. Sure. But how often do you actually need that, compared to the number of times when you deploy an updated config that was working fine on your test system, signal a reload, and off you go? You don't need to wait for it to finish; you'll see errors in the log, if there are any, and most likely there won't (your test system IS virtually identical to live, right?). I have scripts that edit config files and pop off SIGHUPs, usually in response to external events, and they neither need nor want to wait. It's pretty common. For maximum portability, most programs are going to want to continue to respond to SIGHUP, even if they do a systemd-triggered reload some other way. I disagree. You can't just assume you can send a SIGHUP to a daemon for the LOLs. You must first discover the trick in the documentation. The default reaction to SIGHUP is to crash. A daemon (which has detached from the controlling terminal) is within its rights to do just that. Sure it can, and you do need to know what you're sending signals to. But if you're unsure how to reload a daemon, the easiest way to probe it is to send it a SIGHUP (on your test system, of course), and see if it's still running afterwards. And once you know that this process responds thusly to SIGHUP, you can do this many *many* times more, never needing to worry about it. I would guess that there are hundreds, maybe thousands, of times when you can safely fire-and-forget, for every one that you actually need to wait on it - where you need some other action to be delayed until the reload is complete. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
Re: What is elegant way to do configuration on server app
On Fri, Mar 27, 2015 at 7:47 PM, Marko Rauhamaa ma...@pacujo.net wrote: Grant Edwards invalid@invalid.invalid: That sounds rather Windowsesque. The more-or-less standard way to do handle the situation on Unix is to reread the config file when you get a SIGHUP. That, indeed, is the classic Unix way. However, Linux has now moved to systemd: Note however that reloading a daemon by sending a signal (as with the example line above) is usually not a good choice, because this is an asynchronous operation and hence not suitable to order reloads of multiple services against each other. It is strongly recommended to set ExecReload= to a command that not only triggers a configuration reload of the daemon, but also synchronously waits for it to complete. The number of cases where this matters is fairly low. Doing the reload asynchronously is generally sufficient. And even if you have something that waits for the reload to finish, you'll usually fire-and-forget that command anyway. For maximum portability, most programs are going to want to continue to respond to SIGHUP, even if they do a systemd-triggered reload some other way. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
Re: What is elegant way to do configuration on server app
Chris Angelico ros...@gmail.com: The number of cases where this matters is fairly low. Doing the reload asynchronously is generally sufficient. Not sure. Not sure at all. Issues like this occupy a great part of my office hours. And even if you have something that waits for the reload to finish, you'll usually fire-and-forget that command anyway. The command systemctl reload xyz.service is supposed to return when the service is happily running with the updated its configuration. Any failures should be reported with a nonzero exit code from systemctl. For maximum portability, most programs are going to want to continue to respond to SIGHUP, even if they do a systemd-triggered reload some other way. I disagree. You can't just assume you can send a SIGHUP to a daemon for the LOLs. You must first discover the trick in the documentation. The default reaction to SIGHUP is to crash. A daemon (which has detached from the controlling terminal) is within its rights to do just that. Marko -- https://mail.python.org/mailman/listinfo/python-list
Re: What is elegant way to do configuration on server app
On 2015-03-27, Chris Angelico ros...@gmail.com wrote: The same problem occurs with PHP-based web sites, but there you don't get the option of holding over for a SIGHUP, so you're just stuck with uploading a new version of your site file-by-file, or *maybe* attempting an atomic rename of a directory. If you're lucky. I don't think that anybody using PHP can be considered lucky. ;) -- Grant Edwards grant.b.edwardsYow! ANN JILLIAN'S HAIR at makes LONI ANDERSON'S gmail.comHAIR look like RICARDO MONTALBAN'S HAIR! -- https://mail.python.org/mailman/listinfo/python-list
Re: What is elegant way to do configuration on server app
On 2015-03-27, Marko Rauhamaa ma...@pacujo.net wrote: Grant Edwards invalid@invalid.invalid: That sounds rather Windowsesque. The more-or-less standard way to do handle the situation on Unix is to reread the config file when you get a SIGHUP. That, indeed, is the classic Unix way. However, Linux has now moved to systemd: That's a bit of an overstatement. _Some_ distros have switched to systemd. None of my machines use it, and it's very rare in embedded systems. -- Grant Edwards grant.b.edwardsYow! Are we THERE yet? at My MIND is a SUBMARINE!! gmail.com -- https://mail.python.org/mailman/listinfo/python-list
Re: What is elegant way to do configuration on server app
Grant Edwards invalid@invalid.invalid: On 2015-03-27, Marko Rauhamaa ma...@pacujo.net wrote: That, indeed, is the classic Unix way. However, Linux has now moved to systemd: That's a bit of an overstatement. _Some_ distros have switched to systemd. None of my machines use it, and it's very rare in embedded systems. Much less of an overstatement than saying that the Python world has now moved to Python3. RHEL/CentOS/Fedora are there. OpenSuSE is there. Debian is there. Ubuntu is going there. I'm not an apologist of systemd. Just stating the situation. Marko -- https://mail.python.org/mailman/listinfo/python-list
Re: What is elegant way to do configuration on server app
On 2015-03-27, Jerry OELoo oylje...@gmail.com wrote: Make a part of your event loop (assuming your server runs an event loop) that wakes up every N seconds (e.g. every 60 seconds) and checkes the file's modification timestamp again; if it's newer, record that value for future comparisons, then re-read the file for its values. That sounds rather Windowsesque. The more-or-less standard way to do handle the situation on Unix is to reread the config file when you get a SIGHUP. Why use SIGHUP, It's just tradition. Some other seldom-used signal could have been chosen, but way back when somebody chose SIGHUP, and other people followed suit. Does it has something to do with configure file modification? Not intrinsically. It's just a convention in the Unix world that sending SIGHUP to a daemon will cause it to re-read its configuration files. I presume that automagically reading them any time they changed was both too much hassle and possibly dangerous: if a file is being edited, it might get saved in intermediate (broken) states during the editing session. -- Grant Edwards grant.b.edwardsYow! An air of FRENCH FRIES at permeates my nostrils!! gmail.com -- https://mail.python.org/mailman/listinfo/python-list
Re: What is elegant way to do configuration on server app
On Sat, Mar 28, 2015 at 3:28 AM, Grant Edwards invalid@invalid.invalid wrote: I presume that automagically reading them any time they changed was both too much hassle and possibly dangerous: if a file is being edited, it might get saved in intermediate (broken) states during the editing session. Even more so if you have multiple files (look, for instance, at PostgreSQL configs, where you might make simultaneous and connected changes to several related files); if you change one and it's activated before you change another, it might even have security implications - although more likely, it'd cause an outage (when legit connections get rejected because you haven't yet added the permission lines). The same problem occurs with PHP-based web sites, but there you don't get the option of holding over for a SIGHUP, so you're just stuck with uploading a new version of your site file-by-file, or *maybe* attempting an atomic rename of a directory. If you're lucky. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
Re: What is elegant way to do configuration on server app
On Thursday, March 26, 2015 at 4:19:33 PM UTC+8, Jerry OELoo wrote: Hi. I have used python to provide a web service app, it will running 7*24, and it will return some data to client by API. http://jonpy.sourceforge.net/modpy.html Check the page of modpy and django. -- https://mail.python.org/mailman/listinfo/python-list
Re: What is elegant way to do configuration on server app
Jerry OELoo oylje...@gmail.com writes: Currently, I can just think out that I put status into a configure file, and service schedule read this file and get status value, That sounds like a fine start. Some advice: * You may be tempted to make the configuration file executable (e.g. Python code). Resist that temptation; keep it *much* simpler, a non-executable data format. Python's standard library has the ‘configparser’ module URL:https://docs.python.org/3/library/configparser.html to parse and provide the values from a very common configuration file format. Use that unless you have a good reason not to. * Your program can “poll” the configuration file to see whether it has changed. At startup, read the config file's modification timestamp URL:https://docs.python.org/3/library/os.html#os.stat_result.st_mtime. Make a part of your event loop (assuming your server runs an event loop) that wakes up every N seconds (e.g. every 60 seconds) and checkes the file's modification timestamp again; if it's newer, record that value for future comparisons, then re-read the file for its values. Hope that helps. -- \ “For your convenience we recommend courteous, efficient | `\self-service.” —supermarket, Hong Kong | _o__) | Ben Finney -- https://mail.python.org/mailman/listinfo/python-list
What is elegant way to do configuration on server app
Hi. I have used python to provide a web service app, it will running 7*24, and it will return some data to client by API. Now I want to add some extra data in return data, ex, status = 1, and I want this value 1 can be configured, that means I can control that service app return status with 0, 1 or other value, and I want to keep service running always. Currently, I can just think out that I put status into a configure file, and service schedule read this file and get status value, Is there any other elegant way to achieve this? What is standard way in python for this requirement? Thanks! Best Regards Jerry -- Rejoice,I Desire! -- https://mail.python.org/mailman/listinfo/python-list
Re: What is elegant way to do configuration on server app
On 2015-03-26, Ben Finney ben+pyt...@benfinney.id.au wrote: Jerry OELoo oylje...@gmail.com writes: Currently, I can just think out that I put status into a configure file, and service schedule read this file and get status value, That sounds like a fine start. Some advice: * You may be tempted to make the configuration file executable (e.g. Python code). Resist that temptation; keep it *much* simpler, a non-executable data format. Python's standard library has the ‘configparser’ module URL:https://docs.python.org/3/library/configparser.html to parse and provide the values from a very common configuration file format. Use that unless you have a good reason not to. I second the recommendation for configparser for stuff of simple to moderate complexity. If it gets too complex for configparser, you may want to consider JSON, or for even more complex stuff just use plain Python code in your config file (this can be very powerful and expressive, but can also be diffucult to implement safely). * Your program can “poll” the configuration file to see whether it has changed. At startup, read the config file's modification timestamp URL:https://docs.python.org/3/library/os.html#os.stat_result.st_mtime. Make a part of your event loop (assuming your server runs an event loop) that wakes up every N seconds (e.g. every 60 seconds) and checkes the file's modification timestamp again; if it's newer, record that value for future comparisons, then re-read the file for its values. That sounds rather Windowsesque. The more-or-less standard way to do handle the situation on Unix is to reread the config file when you get a SIGHUP. -- Grant Edwards grant.b.edwardsYow! ONE LIFE TO LIVE for at ALL MY CHILDREN in ANOTHER gmail.comWORLD all THE DAYS OF OUR LIVES. -- https://mail.python.org/mailman/listinfo/python-list
