Out of the box dhcplb supports loading DHCP server lists from text files and logging to stderr with glog.
All configuration files supplied to dhcplb (config, overrides and DHCP server files) are watched for changes using fsnotify and hot-reloaded without restarting the server.
Configuration is provided to the program via a JSON file
{
"v4": {
"version": 4, // DHCP operation mode
"listen_addr": "0.0.0.0", // address to bind the receiving socket to
"port": 67, // port to listen on
"packet_buf_size": 1024, // size of buffer to allocate for incoming packet
"update_server_interval": 30, // how often to refresh server list (in seconds)
"free_conn_timeout": 30, // how long to wait after removal before closing a connection to a server (in seconds)
"algorithm": "xid", // balancing algorithm, supported are xid and rr (client hash and roundrobin)
"host_sourcer": "file:hosts-v4.txt", // load DHCP server list from hosts-v4.txt
"rc_ratio": 0, // what percentage of requests should go to RC servers
"throttle_cache_size": 1024, // cache size for number of throttling objects for unique clients
"throttle_cache_rate": 128, // rate value for throttling cache invalidation (per second)
"throttle_rate_per_conn": 256 // rate value for request per client (per second)
},
... (same options for "v6") ...dhcplb supports configurable overrides for individual machines. A MAC address
can be configured to point to a specific DHCP server IP or to a "tier" (group)
of servers.
Overrides are defined in a JSON file and the path is passed to dhcplb as the
command-line arg -overrides.
{
"v4": {
"12:34:56:78:90:ab": {
"host": "173.252.90.132"
},
"fe:dc:ba:09:87:65": {
"tier": "myGroup"
}
},
"v6": {
}
}With this overrides file, DHCPv4 requests coming from MAC 12:34:56:78:90:ab
will be sent to the DHCP server at 173.252.90.132, and requests from MAC
fe:dc:ba:09:87:65 will be sent to the tier of servers myGroup (a server will
be picked according to the balancing algorithm's selection from the list of
servers returned by the GetServersFromTier(tier string) function of the
DHCPServerSourcer being used.)
dhcplb keeps track of the request rate per second for each client.
It can be set through throttle_rate_per_conn configuration parameter.
Requests exceeding this limit will be logged and dropped. For 0 or negative
values no throttling will be done, and no cache will be created.
An LRU cache is used to keep track of rate information for each client. Cache
size can be set through throttle_cache_size. To prevent fast cache
invalidation from malicious clients, dhcplb also keeps track of the number of
new clients being added to the cache (per second). This behavior can be set
through throttle_cache_rate configuration parameter. For 0 or negative values
no cache rate limiting will be done.
dhcplb supports sending a percentage of requests to servers marked as RC and
the rest to Stable servers.
This percentage is configurable via the rc_ratio JSON option.
Using the A/B testing functionality requires providing two lists of servers,
this can be done via the built in filesourcer by specifying the host_sourcer
option as "file:<stable_path>,<rc_path>"
It's possible to extend dhcplb to modify the way it fetches the list of
DHCP servers, or have a different logging implementation, or add different
balancing algorithms.
At the moment this is a bit complex but we will work on ways to make it easier.
Adding a new algorithm can be done by implementing something that matches
the dhcpBalancingAlgorithm interface:
type dhcpBalancingAlgorithm interface {
selectServerFromList(list []*DHCPServer, message *DHCPMessage) (*DHCPServer, error)
selectRatioBasedDhcpServer(message *DHCPMessage) (*DHCPServer, error)
updateStableServerList(list []*DHCPServer) error
updateRCServerList(list []*DHCPServer) error
setRCRatio(ratio uint32)
}Then add it to the algorithms map in the configSpec.algorithm function, in
the config.go file.
More configuration options can be added to the config JSON file using the
ConfigProvider interface:
type ConfigProvider interface {
NewHostSourcer(sourcerType, args string, version int) (DHCPServerSourcer, error)
ParseExtras(extras json.RawMessage) (interface{}, error)
}The NewHostSourcer function is passed values from the host_sourcer config option
with the sourcerType being the part of the string before the : and args the
remaining portion. ex: file:hosts-v4.txt,hosts-v4-rc.txt will have sourcerType="file"
and args="hosts-v4.txt,hosts-v4-rc-txt".
The default Config loader is able to instantiate a FileSourcer by itself, so
NewHostSourcer can simply return nil, nil unless you are using a custom sourcer
implementation.
Any struct can be returned from the ParseExtras function and used elsewhere in
the code via the Extras member of a Config struct.
If you want to change the way dhcplb sources the list of DHCP servers (for
example you want to source them from a backend system like a database) you can
have something implementing the DHCPServerSourcer interface:
type DHCPServerSourcer interface {
GetStableServers() ([]*DHCPServer, error)
GetRCServers() ([]*DHCPServer, error)
// get servers from a specific named group (this is used with overrides)
GetServersFromTier(tier string) ([]*DHCPServer, error)
}Then implement your own ConfigProvider interface and make it return a
DHCPServerSourcer. Then in the main you can replace NewDefaultConfigProvider
with your own ConfigProvider implementation.
$ ./dhcplb -h
Usage of ./dhcplb:
-alsologtostderr
log to standard error as well as files
-config string
Path to JSON config file
-log_backtrace_at value
when logging hits line file:N, emit a stack trace (default :0)
-log_dir string
If non-empty, write log files in this directory
-logtostderr
log to standard error instead of files
-overrides string
Path to JSON overrides file
-pprof int
Port to run pprof HTTP server on
-stderrthreshold value
logs at or above this threshold go to stderr
-v value
log level for V logs
-version int
Run in v4/v6 mode (default 4)
-vmodule value
comma-separated list of pattern=N settings for file-filtered logging