Templates
January 6, 2020 ยท View on GitHub
Templates define a single application configuration template.
Templates are stored under the /etc/confd/templates directory by default.
Templates are written in Go's text/template.
Template Functions
map
creates a key-value map of string -> interface{}
{{$endpoint := map "name" "elasticsearch" "private_port" 9200 "public_port" 443}}
name: {{index $endpoint "name"}}
private-port: {{index $endpoint "private_port"}}
public-port: {{index $endpoint "public_port"}}
specifically useful if you use a sub-template and you want to pass multiple values to it.
base
Alias for the path.Base function.
{{with get "/key"}}
key: {{base .Key}}
value: {{.Value}}
{{end}}
exists
Checks if the key exists. Return false if key is not found.
{{if exists "/key"}}
value: {{getv "/key"}}
{{end}}
get
Returns the KVPair where key matches its argument. Returns an error if key is not found.
{{with get "/key"}}
key: {{.Key}}
value: {{.Value}}
{{end}}
cget
Returns the KVPair where key matches its argument and the value has been encrypted. Returns an error if key is not found.
{{with cget "/key"}}
key: {{.Key}}
value: {{.Value}}
{{end}}
gets
Returns all KVPair, []KVPair, where key matches its argument. Returns an error if key is not found.
{{range gets "/*"}}
key: {{.Key}}
value: {{.Value}}
{{end}}
cgets
Returns all KVPair, []KVPair, where key matches its argument and the values have been encrypted. Returns an error if key is not found.
{{range cgets "/*"}}
key: {{.Key}}
value: {{.Value}}
{{end}}
getv
Returns the value as a string where key matches its argument or an optional default value. Returns an error if key is not found and no default value given.
value: {{getv "/key"}}
With a default value
value: {{getv "/key" "default_value"}}
cgetv
Returns the encrypted value as a string where key matches its argument. Returns an error if key is not found.
value: {{cgetv "/key"}}
getvs
Returns all values, []string, where key matches its argument. Returns an error if key is not found.
{{range getvs "/*"}}
value: {{.}}
{{end}}
cgetvs
Returns all encrypted values, []string, where key matches its argument. Returns an error if key is not found.
{{range cgetvs "/*"}}
value: {{.}}
{{end}}
getenv
Wrapper for os.Getenv. Retrieves the value of the environment variable named by the key. It returns the value, which will be empty if the variable is not present. Optionally, you can give a default value that will be returned if the key is not present.
export HOSTNAME=`hostname`
hostname: {{getenv "HOSTNAME"}}
With a default value
ipaddr: {{getenv "HOST_IP" "127.0.0.1"}}
datetime
Alias for time.Now
# Generated by confd {{datetime}}
Outputs:
# Generated by confd 2015-01-23 13:34:56.093250283 -0800 PST
# Generated by confd {{datetime.Format "Jan 2, 2006 at 3:04pm (MST)"}}
Outputs:
# Generated by confd Jan 23, 2015 at 1:34pm (EST)
See the time package for more usage: http://golang.org/pkg/time/
split
Wrapper for strings.Split. Splits the input string on the separating string and returns a slice of substrings.
{{ $url := split (getv "/deis/service") ":" }}
host: {{index $url 0}}
port: {{index $url 1}}
toUpper
Alias for strings.ToUpper Returns uppercased string.
key: {{toUpper "value"}}
toLower
Alias for strings.ToLower. Returns lowercased string.
key: {{toLower "Value"}}
json
Returns an map[string]interface{} of the json value.
lookupSRV
Wrapper for net.LookupSRV. The wrapper also sorts the SRV records alphabetically by combining all the fields of the net.SRV struct to reduce unnecessary config reloads.
{{range lookupSRV "mail" "tcp" "example.com"}}
target: {{.Target}}
port: {{.Port}}
priority: {{.Priority}}
weight: {{.Weight}}
{{end}}
base64Encode
Returns a base64 encoded string of the value.
key: {{base64Encode "Value"}}
base64Decode
Returns the string representing the decoded base64 value.
key: {{base64Decode "VmFsdWU="}}
Add keys to etcd
etcdctl set /services/zookeeper/host1 '{"Id":"host1", "IP":"192.168.10.11"}'
etcdctl set /services/zookeeper/host2 '{"Id":"host2", "IP":"192.168.10.12"}'
Create the template resource
[template]
src = "services.conf.tmpl"
dest = "/tmp/services.conf"
keys = [
"/services/zookeeper/"
]
Create the template
{{range gets "/services/zookeeper/*"}}
{{$data := json .Value}}
id: {{$data.Id}}
ip: {{$data.IP}}
{{end}}
Advanced Map Traversals
Once you have parsed the JSON, it is possible to traverse it with normal Go
template functions such as index.
A more advanced structure, like this:
{
"animals": [
{"type": "dog", "name": "Fido"},
{"type": "cat", "name": "Misse"}
]
}
It can be traversed like this:
{{$data := json (getv "/test/data/")}}
type: {{ (index $data.animals 1).type }}
name: {{ (index $data.animals 1).name }}
{{range $data.animals}}
{{.name}}
{{end}}
jsonArray
Returns a []interface{} from a json array such as ["a", "b", "c"].
{{range jsonArray (getv "/services/data/")}}
val: {{.}}
{{end}}
ls
Returns all subkeys, []string, where path matches its argument. Returns an empty list if path is not found.
{{range ls "/deis/services"}}
value: {{.}}
{{end}}
lsdir
Returns all subkeys, []string, where path matches its argument. It only returns subkeys that also have subkeys. Returns an empty list if path is not found.
{{range lsdir "/deis/services"}}
value: {{.}}
{{end}}
dir
Returns the parent directory of a given key.
{{with dir "/services/data/url"}}
dir: {{.}}
{{end}}
join
Alias for the strings.Join function.
{{$services := getvs "/services/elasticsearch/*"}}
services: {{join $services ","}}
replace
Alias for the strings.Replace function.
{{$backend := getv "/services/backend/nginx"}}
backend = {{replace $backend "-" "_" -1}}
seq
seq creates a sequence of integers. It's named and used as GNU's seq.
seq takes the first and the last element as arguments. So seq 3 5 will generate [3,4,5]
{{- range $i := seq 0 (len "/foo/bar")}}
{{- if $i}},{{end}}
{{$i}}
lookupIP
Wrapper for net.LookupIP function. The wrapper also sorts (alphabeticaly) the IP addresses. This is crucial since in dynamic environments DNS servers typically shuffle the addresses linked to domain name. And that would cause unnecessary config reloads.
{{range lookupIP "some.host.local"}}
server {{.}};
{{end}}
atoi
Alias for the strconv.Atoi function.
{{seq 1 (atoi (getv "/count"))}}
Example Usage
etcdctl set /nginx/domain 'example.com'
etcdctl set /nginx/root '/var/www/example_dotcom'
etcdctl set /nginx/worker_processes '2'
etcdctl set /app/upstream/app1 "10.0.1.100:80"
etcdctl set /app/upstream/app2 "10.0.1.101:80"
/etc/confd/templates/nginx.conf.tmpl
worker_processes {{getv "/nginx/worker_processes"}};
upstream app {
{{range getvs "/app/upstream/*"}}
server {{.}};
{{end}}
}
server {
listen 80;
server_name www.{{getv "/nginx/domain"}};
access_log /var/log/nginx/{{getv "/nginx/domain"}}.access.log;
error_log /var/log/nginx/{{getv "/nginx/domain"}}.log;
location / {
root {{getv "/nginx/root"}};
index index.html index.htm;
proxy_pass http://app;
proxy_redirect off;
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
}
}
Output: /etc/nginx/nginx.conf
worker_processes 2;
upstream app {
server 10.0.1.100:80;
server 10.0.1.101:80;
}
server {
listen 80;
server_name www.example.com;
access_log /var/log/nginx/example.com.access.log;
error_log /var/log/nginx/example.com.error.log;
location / {
root /var/www/example_dotcom;
index index.html index.htm;
proxy_pass http://app;
proxy_redirect off;
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
}
}
Complex example
This examples show how to use a combination of the templates functions to do nested iteration.
Add keys to etcd
etcdctl mkdir /services/web/cust1/
etcdctl mkdir /services/web/cust2/
etcdctl set /services/web/cust1/2 '{"IP": "10.0.0.2"}'
etcdctl set /services/web/cust2/2 '{"IP": "10.0.0.4"}'
etcdctl set /services/web/cust2/1 '{"IP": "10.0.0.3"}'
etcdctl set /services/web/cust1/1 '{"IP": "10.0.0.1"}'
Create the template resource
[template]
src = "services.conf.tmpl"
dest = "/tmp/services.conf"
keys = [
"/services/web"
]
Create the template
{{range $dir := lsdir "/services/web"}}
upstream {{base $dir}} {
{{$custdir := printf "/services/web/%s/*" $dir}}{{range gets $custdir}}
server {{$data := json .Value}}{{$data.IP}}:80;
{{end}}
}
server {
server_name {{base $dir}}.example.com;
location / {
proxy_pass {{base $dir}};
}
}
{{end}}
Output:/tmp/services.conf
upstream cust1 {
server 10.0.0.1:80;
server 10.0.0.2:80;
}
server {
server_name cust1.example.com;
location / {
proxy_pass cust1;
}
}
upstream cust2 {
server 10.0.0.3:80;
server 10.0.0.4:80;
}
server {
server_name cust2.example.com;
location / {
proxy_pass cust2;
}
}
Go's text/template package is very powerful. For more details on it's capabilities see its documentation.