cached is a daemon for caching big files(video, in most cases) from backends to frontends.

How it works

Daemon works at frontends, looks into logfile of requests that passed to backend and download popular files to frontends. It uses MySQL database to keep scoreboard and a table with list of files, that already cached on frontends.

Depending on your architecture it can work in two modes(dmode):

• Round-Robin - download all popular files on all frontends.
• Sharding - download files only whith my fe_id setting.

Installation

Requirement packages:

• Mysql client libs
• Pcre (pcreposix)
• Libcurl
• Gamin(fam)

Download cached-0.4.tar.gz

On the frontend server:

tar -xzvf cached-0.4.tar.gz
cd cached-0.4
./configure
make
make install

On MySQL server:

mysql < cached.sql

Configuration

/etc/cached/cached.conf:

# PID file location
pid = "/var/run/cached.pid";

# user
user = "www-data";

# Frontend ID
fe_id = 77;

# if file requests >= cache_req_count, file will be cached
cache_req_count = 10;

# Download workers
workers = 3;

# Pass a long as parameter containing the maximum time in seconds 
# that you allow the libcurl transfer operation to take. 
curl_timeout = 600;

# Connection time out, in seconds 
curl_connect_timeout = 10;

# Log
log = "/var/log/cached/cached.log";

# LogLevel
# 1 - ERROR, 2 - WARN, 3 - DEBUG
log_level = 3;

# access log for processing
access_log = "/var/log/nginx/proxypass.log";

# cached-video path (without "/" on end)
cache_store = "/tmp/nginx";

# Backends
upstreams = [ "10.100.1.61",
          "192.168.100.150",
              "10.100.1.63"];

# if upstream failed, it will be marked as dead on upstream_dead_timeout seconds.
upstream_dead_timeout = 60;

# Logfile regex (in pcre format)
# Matches:
# 1 - datetime in msec
# 2 - size
# 3 - last_modified
# 4 - status
# 5 - file path
log_regex = "(\\d+)\\.\\d+\\|(\\d+)\\|(.+)\\|(200|206|304|499)\\|GET \\/(\\S+\.flv|\\S+.mp4).*";

# Last_modififed date format (in MySQL from_str format)
lm_format = "%a, %d %b %Y %H:%i:%S GMT";

# MySQL settings
mysql_host = "somemysqlserver";
mysql_port = 3306;
mysql_db   = "cached";
mysql_login = "cached";
mysql_password = "cached";

# Download mode
# 1 - download only my videos (SHARDING MODE)
# 2 - download all popular (ROUND ROBIN MODE)

dmode = 1;

/etc/nginx/nginx.conf:

...
        location ~ \.mp4 {
               root    /tmp/nginx;
               open_file_cache_errors  off;
               error_page      404 = @getmp4;
               }

        location @getmp4 {
               proxy_pass http://10.100.1.61;
               error_page      404 = /errors/404.html;
                access_log  /var/log/nginx/proxypass.log vcache_new;
               }

...

Running

In our example we have 3 backend servers(10.100.1.61 ...), so we need to run Web-server on, at least, one backend. Run nginx on frontend and start cached:

/etc/init.d/cached start

Here what we got in logfile:

tail -f /var/log/cached/cached.log
[Sat Jan  5 01:51:31 2013] [ERROR] (master)4986# All workers started
[Sat Jan  5 01:51:31 2013] [ERROR] (downloader)4989# Connected to MySQL.
[Sat Jan  5 01:51:31 2013] [DEBUG] (downloader)4989# Upstream: 10.100.1.61, active: 1
[Sat Jan  5 01:51:31 2013] [ERROR] (fparser)4987# Connected to MySQL.
[Sat Jan  5 01:51:31 2013] [DEBUG] (downloader)4989# Upstream: 10.100.1.62, active: 1
[Sat Jan  5 01:51:31 2013] [DEBUG] (fparser)4987# FAMExists
[Sat Jan  5 01:51:31 2013] [DEBUG] (fparser)4987# Wow, fresh meat...(Gamin)
[Sat Jan  5 01:51:31 2013] [DEBUG] (fparser)4987# FAMEndExist
[Sat Jan  5 01:51:31 2013] [WARN] (fparser)4987# Unknown event (Gamin): FAMEndExist
[Sat Jan  5 01:51:32 2013] [DEBUG] (worker #2)4993# Queue "/workers_queue":
        - stores at most 10 messages
        - large at most 8192 bytes each
        - currently holds 0 messages

That's it, cached started.

Helper scripts

We need to clean our tables periodically, there's a crontab in root cached_scheduler, place it near your database.