Flavors

A flavor refers to a specific mcrouter configuration. Flavor configs specify command line arguments for running mcrouter. They configure which config file to use, and various other startup parameters. For a full list of mcrouter startup options see Startup Options.

In practice, flavors are JSON files that contains all (or some) of the command-line options one would use to run mcrouter. They are commonly used to avoid long command-lines and/or to save configs. In flavors, we use internal name instead of command line option. In most cases it is the same as long option name with dashes replaced with underscores (i.e. --disable-reload-configs becomes disable_reload_configs).

There are two kinds of flavors: libmcrouter flavors (or simply flavors) and standalone mcrouter flavors, which are described in details bellow.

libmcrouter flavor

The libmcrouter flavor (or simply flavor) config specifies common mcrouter options. See the example bellow:

{
  "options": {
    "default_route": "/region1/cluster1/",
    "config_file": "mcrouter_config.json"
  }
}

Assuming the above config is saved in a file named myflavor, the command mcrouter myflavor -p 5000 is equivalent to mcrouter --default-route='/region1/cluster1/' --config-file='mcrouter_config.json' -p 5000.

standalone flavor

The standalone flavor config can be used to specify parameters related to the mcrouter process. See the example bellow:

{
  "libmcrouter_options": {
    "default_route": "/region1/cluster1/",
    "config_file": "mcrouter_config.json"
  },
  "standalone_options": {
    "log_file": "/var/logs/mcrouter-web.log",
    "ports": "8888"
  }
}

Assuming the above config is saved in a file named myflavor-standalone, the command mcrouter myflavor is equivalent to mcrouter --default-route='/region1/cluster1/' --config-file='mcrouter_config.json' --log-file='/var/logs/mcrouter-web.log' -p 8888. There are some things from the above example that are worth mentioning:

• Althought the file is named myflavor-standalone, the flavor named informed is simply myflavor. That's a rule for standalone flavors.
• The "libmcrouter_options" object is optional for standalone flavor configs. If present, these options will be used to replace options read from the libmcrouter flavor config for that particular flavor.
• The following options are standalone options and should be informed in the standalone_options object of the standalone flavor file: log_file, debug_level, ports, ssl_ports, listen_sock_fd, pidfile, background, managed, fdlimit, max_global_outstanding_reqs, max_client_outstanding_reqs, requests_per_read, enable_failure_logging. All the other options should go into the libmcrouter_options object or in the libmcrouter flavor file.

Usage

To use a flavor, simply inform its path (without any suffixes, i.e. "-standalone") to mcrouter command line:

$ mcrouter /path/to/flavor

Behavior

If just one of the flavor files are present (either the standalone or the libmcrouter file), the behavior is pretty straight forward: the options present in that file are loaded and applied. (note that the suffix "-standalone" must be present to the standalone flavor file name but should never be specified in the command-line).
If the user has both files (the libmcrouter and the standalone flavor files) mcrouter first loads the options present in the libmcrouter flavor file. Then, mcrouter locates the standalone flavor file by appending the suffix "-standalone" to the end of the informed flavor file name. It is then loaded and, any options found in the "libmcrouter_options" object overwrites options with the same name read from "options" object at the libmcrouter flavor file.

Example

Find bellow a simply scenario that illustrates how mcrouter handles flavors:

File /var/mcrouter/myflavor:

{
  "options": {
    "default_route": "/region1/cluster1/",
    "config_file": "mcrouter_config.json"
  }
}

File /var/mcrouter/myflavor-standalone:

{
  "libmcrouter_options": {
    "default_route": "/region3/"
  },
  "standalone_options": {
    "ports": "5000"
  }
}

Given that the above files are properly saved to disk at the locations specified, the following two commands are equivalent:

$ mcrouter /var/mcrouter/myflavor

$ mcrouter --default-route='/region3/' --config-file='mcrouter_config.json' -p 5000

Note: The default_route option present in the libmcrouter_options object in the standalone flavor file, overwrote the default_route option present in the libmcrouter flavor file.