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---
title: "Leveraging yaml with cfengine"
date: 2018-09-25
description: How to leverage yaml inventory files with cfengine
tags:
- cfengine
---
## Introduction
CFEngine has core support for JSON and YAML. You can use this support to read, access, and merge JSON and YAML files and use these to keep policy files internal and simple. You
access the data using the usual cfengine standard primitives.
The use case bellow lacks a bit or error control with argument validation, it will fail miserably if the YAML file is invalid.
## Example yaml
In `cmdb/hosts/andromeda.yaml` we describe some properties of a host named andromeda:
```yaml
domain: adyxax.org
host_interface: dummy0
host_ip: "10.1.0.255"
tunnels:
collab:
port: 1195
ip: "10.1.0.15"
peer: "10.1.0.14"
remote_host: collab.example.net
remote_port: 1199
legend:
port: 1194
ip: "10.1.0.3"
peer: "10.1.0.2"
remote_host: legend.adyxax.org
remote_port: 1195
```
## Reading the yaml
I am bundling the values in a common bundle, accessible globally. This is one of the first bundles processed in the order my policy files are loaded. This is just an extract, you can load multiple files and merge them to distribute common
settings :
```yaml
bundle common g
{
vars:
has_host_data::
"host_data" data => readyaml("$(sys.inputdir)/cmdb/hosts/$(sys.host).yaml", 100k);
classes:
any::
"has_host_data" expression => fileexists("$(sys.inputdir)/cmdb/hosts/$(sys.host).yaml");
}
```
## Using the data
### Cfengine agent bundle
We access the data using the global g.host_data variable, here is a complete example :
```yaml
bundle agent openvpn
{
vars:
any::
"tunnels" slist => getindices("g.host_data[tunnels]");
files:
any::
"/etc/openvpn/common.key"
create => "true",
edit_defaults => empty,
perms => system_owned("440"),
copy_from => local_dcp("$(sys.inputdir)/templates/openvpn/common.key.cftpl"),
classes => if_repaired("openvpn_common_key_repaired");
methods:
any::
"any" usebundle => install_package("$(this.bundle)", "openvpn");
"any" usebundle => openvpn_tunnel("$(tunnels)");
services:
linux::
"openvpn@$(tunnels)"
service_policy => "start",
classes => if_repaired("tunnel_$(tunnels)_service_repaired");
commands:
any::
"/usr/sbin/service openvpn@$(tunnels) restart"
classes => if_repaired("tunnel_$(tunnels)_service_repaired"),
ifvarclass => "openvpn_common_key_repaired";
reports:
any::
"$(this.bundle): common.key repaired" ifvarclass => "openvpn_common_key_repaired";
"$(this.bundle): $(tunnels) service repaired" ifvarclass => "tunnel_$(tunnels)_service_repaired";
}
bundle agent openvpn_tunnel(tunnel)
{
classes:
any::
"has_remote" and => { isvariable("g.host_data[tunnels][$(tunnel)][remote_host]"),
isvariable("g.host_data[tunnels][$(tunnel)][remote_port]") };
files:
any::
"/etc/openvpn/$(tunnel).conf"
create => "true",
edit_defaults => empty,
perms => system_owned("440"),
edit_template => "$(sys.inputdir)/templates/openvpn/tunnel.conf.cftpl",
template_method => "cfengine",
classes => if_repaired("openvpn_$(tunnel)_conf_repaired");
commands:
any::
"/usr/sbin/service openvpn@$(tunnel) restart"
classes => if_repaired("tunnel_$(tunnel)_service_repaired"),
ifvarclass => "openvpn_$(tunnel)_conf_repaired";
reports:
any::
"$(this.bundle): $(tunnel).conf repaired" ifvarclass => "openvpn_$(tunnel)_conf_repaired";
"$(this.bundle): $(tunnel) service repaired" ifvarclass => "tunnel_$(tunnel)_service_repaired";
}
```
### Template file
Templates can reference the g.host_data too, like in the following :
```cfg
[%CFEngine BEGIN %]
proto udp
port $(g.host_data[tunnels][$(openvpn_tunnel.tunnel)][port])
dev-type tun
dev tun_$(openvpn_tunnel.tunnel)
comp-lzo
script-security 2
ping 10
ping-restart 20
ping-timer-rem
persist-tun
persist-key
cipher AES-128-CBC
secret /etc/openvpn/common.key
ifconfig $(g.host_data[tunnels][$(openvpn_tunnel.tunnel)][ip]) $(g.host_data[tunnels][$(openvpn_tunnel.tunnel)][peer])
user nobody
[%CFEngine centos:: %]
group nobody
[%CFEngine ubuntu:: %]
group nogroup
[%CFEngine has_remote:: %]
remote $(g.host_data[tunnels][$(openvpn_tunnel.tunnel)][remote_host]) $(g.host_data[tunnels][$(openvpn_tunnel.tunnel)][remote_port])
[%CFEngine END %]
```
## References
- https://docs.cfengine.com/docs/master/examples-tutorials-json-yaml-support-in-cfengine.html
- https://docs.cfengine.com/docs/3.10/reference-functions-readyaml.html
- https://docs.cfengine.com/docs/3.10/reference-functions-mergedata.html
|
