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Configuration File system


Config-fs is a key/value backed configuration file system. The daemon process synchronizes the content found in K/V store, converting the keys into files / directories and so forth. Naturally any changes which are made at the K/V end are propagated downstream to the config file system.

Current Status

  • Replication of the K/V store to the configuration directory is working
  • The watcher service needs to be completed and integrated - thus allowing for write access to the backend (though not a priority at the moment)
  • The dynamic resources work, but requires a code clean up, a review and no doubt a number of bug fixes
  • Presently only supports etcd for the K/V store and consul for discovery

Configuration

   [jest@starfury config-fs]$ stage/config-fs --help
   Usage of stage/config-fs:
     -alsologtostderr=false: log to standard error as well as files
     -delete_on_exit=false: delete all configuration on exit
     -delete_stale=false: delete stale files, i.e files which do not exists in the backend k/v store
     -discovery="": the service discovery backend being used
     -interval=900: the default interval for performed a forced resync
     -log_backtrace_at=:0: when logging hits line file:N, emit a stack trace
     -log_dir="": If non-empty, write log files in this directory
     -logtostderr=false: log to standard error instead of files
     -mount="/config": the mount point for the K/V store
     -pre_sync=true: wheather or not to perform a initial config sync against the backend
     -read_only=true: wheather or not the config store of read-only
     -root="/": the root within the k/v store to base the config on
     -stderrthreshold=0: logs at or above this threshold go to stderr
     -store="etcd://localhost:4001": the url for key / value store
     -v=0: log level for V logs
     -vmodule=: comma-separated list of pattern=N settings for file-filtered logging

Configuration Root

By default the configuration directory is build from root "/", the -root=KEY can override this though. A use case for this would be hide expose only a subsection of the k/v store. For example, we can expose /prod/app/config directory to /config while hiding everything underneath; note: ALL dynamic configs take keys from root "/", so in our case we expose the config files, which placing the credentials, values, config etc which the dynamic config reference hidden beneath.

Dynamic Config

Dynamic config works in a similar vain to confd. It presently supported the following methods when templating the file. Dynamic content is defined by simply prefixed the value of the K/V with "\$TEMPLATE$" (yes, not the most sophisticated means, but will work for now), note the prefix is removed from the actual content.

{{ service "frontend_http" }}

The method search the discovery provider for a service, returning the following struct

type Service struct {
    /* the descriptive for the service */
    Name string
    /* the tags associated to the service */
    Tags []string
}

{{ $service := service "frontend_http" }}
{{ $service.Tags }}

{{ services }}

Returns a array of all services from the discovery provider

{{ range services }}
Name: {{ .Name }}, Tags: {{ print "," | join .Tags }}
{{ end }}

{{ endpoints "frontend_http" }}

Similar to the above method, it returns an array of <IPADDRESS>:<PORT> endpoints in the service request.

The struct returned

type Endpoint struct {
  ID string
  /* the name of the service */
  Name string
  /* the ip address of the service */
  Address string
  /* the port the service is running on */
  Port int
}

{{ range getl "/services/frontends/" }}
frontend {{ base .Path }}
  bind *: {{ getv "/services/frontend/port" }}
  mode http
  default_backend {{ base .Path }}

backend {{ base .Path }}
  mode http
  balance roundrobin
  option forwardfor
  http-request set-header X-Forwarded-Port %[dst_port]
  http-request add-header X-Forwarded-Proto https if { ssl_fc }
{{ range service .Path }}  server {{.Address}}_{{.Port}} {{.Address}}:{{.Port}}{{printf "\n"}}{{end}}
{{ end }}

or

{{range endpoints "frontend_http"}}  server {{.Address}}_{{.Port}} {{.Address}}:{{.Port}}{{printf "\n"}}{{end}}
# Producing something like
server 10.241.1.75_31002 10.241.1.75:31002
server 10.241.1.75_31001 10.241.1.75:31001

{{ endpointsl "frontend_http" }}

A helper method for the one above, it simply hands back the endpoints as a array of strings

{{$services := endpoints "frontend_http"}}
services: {{join $services ","}}

{{ get "/this/is/a/key/im/interested/in" }}

The Get() method is used to retrieve and watch a key/pair with in the K/V store.

type Node struct {
    /* the path for this key */
    Path string
    /* the value of the key */
    Value string
    /* the type of node it is, directory or file */
    Directory bool
}

{{$node := get "/prod/config/database/password" }}
{{$node.Path}} {{$node.Value}}

{{ gets "/this/is/a/key/im/interested/in" }}

Returns an array of keypairs - essentially a list of children (files/directories) under the path

{{ range gets "/services/http/frontends" }}
{{ service

{{ end }}

{{ getv "/this/is/a/key/im/interested/in" }}

The GetValue() method is used to retrieve 'value' of a key with in the K/V store.

username: product_user
password: {{ getv "/prod/config/db/password" }}

{{ getr "/this/is/a/key/im/interested/" }}

The GetList() method is used to produce an aray of child keys (excluding directories) under the path specified.

Lets just assume for some incredible reason we are using the directory /prod/config/zookeeper to keep a list of zookeepers ... i.e. /prod/config/zookeeper/zoo101 => 10.241.1.100, /prod/config/zookeeper/zoo102 => 10.241.1.101 etc.

{{range getr "/prod/config/zookeeper"}}
server {{.Value}}{{end}

contained

Checks to see if a value is inside an array i.e. check if a tag is present in a service

{{ if "haproxy" | contained .Tags }}
Not really a fan of this pipeline thing ... give me ERB any day
{{end}}

json

Takes a argument, hopefully some json string and unmarshalls string in a map[string]value

jsona

Takes a json string and unmarshalls string in an array of map[string]value

Additional (well add example later)

"base":      path.Base,
"dir":       path.Dir,
"split":     strings.Split,
"getenv":    os.Getenv,
"join":      strings.Join}
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