intermission is a bit of OpenResty magic written in Lua to help you perform zero down time maintenance. At 37signals we use this to perform application maintenance with limited/no impact to the user. In our use cases, we "hold" the users requests for less than 10 seconds while we do our database maintenance via mysql_role_swap. The user sees a single long request, and things carry right along.
Put an incoming web request on hold long enough to do bad things behind the scenes. Release the incoming requests in the same order they were received. Has zero dependencies.
Requests can only be paused as long the device sitting in front of it will allow. If you have haproxy deployed in front of your Nginx instance, make sure to check your "srvtimeout" values.
- Run
vagrant up(This will download the image, boot it, and compile and install openresty) - Run
vagrant ssh - Run
tail -f /usr/local/openresty/nginx/logs/intermission-error.log - Hit http://localhost:8080 (you should see google)
- Hit http://localhost:8080/_intermission/enable.
- Hit http://localhost:8080/_intermission/status. (you should see "Pause Enabled")
- Hit http://localhost:8080 (you should see nothing)
- Hit http://localhost:8080/_intermission/disable.
- (Your request should have gone through now...)
If you have many virtual hosts running on one nginx instance, you most likely don't want to pause all of them. You can scope the pause to a virtual server by setting $app_name in the server directive of the virtual host:
server {
# Stick the app name in an nginx variable for use with intermission.
# Since we want it set for all of the app requests, set it at the
# server level.
set $app_name <%= @app_name %>;
# ... rest of config ...
}
What if your health check isn't at /up? Simply override the $intermission_health_check_path in the nginx config. What if you want a longer max pause time? Override $intermission_max_time in the nginx config. What if there's an external service like Pingdom and you always want their checks to succeed? Override $intermission_privileged_user_agent in the nginx config:
server {
listen 80;
server_name localhost;
location / {
error_log logs/intermission-error.log debug;
set $intermission_max_time 300; #seconds
set $intermission_health_check_path /up/database;
set $intermission_privileged_user_agent "Pingdom";
access_by_lua_file intermission/intermission.lua;
proxy_pass http://google.com;
}
# Hit /_intermission/[status,disable,enable]
location /_intermission {
content_by_lua_file intermission/intermission_helpers.lua;
}
}
The fastest way to get help is to send an email to intermission@librelist.com. Github issues and pull requests are checked regularly.
Pull requests with passing tests (there are no tests!) are welcomed and appreciated.
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