consul-template: process once if tag filter exists

[DJ Enriquez]

Hello,

I'm trying to set up a template that will handle filtering a service based on multiple tags.

For example: We have 7 services named "Foo" registered in Consul. They are tagged accordingly:

1. dev, proxied, ab
2. dev, proxied
3. test, ab
4. test, proxied, ab
5. test, proxied, ab
6. test, proxied, ab
7. prod, proxied

How do I set up a template to filter all "Foo"s to check if any are tagged "test", "proxied", and "ab"? And if so, to process something ONLY ONCE.

{{range services}}

{{range service .Name}}

{{if .Tags.Contains "proxied"}}{{if and (.Tags.Contains "test) (.Tags.Contains "proxied)}}

//{{.Name}}: YOU HAVE A SERVICE TAGGED "test" "proxied" and "ab"!!

{{end}}{{end}}

{{end}}

{{end}}

The template above will produce the following

//Foo: YOU HAVE A SERVICE TAGGED "test" "proxied" and "ab"!!

//Foo: YOU HAVE A SERVICE TAGGED "test" "proxied" and "ab"!!

//Foo: YOU HAVE A SERVICE TAGGED "test" "proxied" and "ab"!!

It produced it three times because there are three instances of Foo tagged "test" "proxied" and "ab". How do i get this to do it once??

[Michael Fischer]

You can set variables in templates - maybe something like this?

{{range services}}

{{$found := "no"}}

{{range service .Name}}

{{if and ($found eq "no") (.Tags.Contains "test") (.Tags.Contains "proxied") (.Tags.Contains "ab")}}

//{{.Name}}: YOU HAVE A SERVICE TAGGED "test" "proxied" and "ab"!!

{{$found := "yes"}}

{{end}}

{{end}}

{{end}}

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[DJ Enriquez]

Thanks for the reply Michael, that solution works great in the scope of that problem. However, realistically, I need an ELSE clause that happens if NONE of the services satisfy that requirement, and I need that ELSE statement to write once.

Pseudo-code may explain it better:

for(int i = 0; i < serviceFoo.Length; i++)

{

     if(service.Foo[i].Contains("test" and "proxied" and "ab"))

     {

           log("Found it!");

           break;

     }

     if(i == serviceFoo.Length -1) //Were at the last item and it was not found

     {

           log("This does not exist");

     }

}

So this would write just one entry. Is this possible in go-templating?

[Michael Fischer]

I think you can do it using the "$found" variable by comparing its value after the range iteration completes.  Have you tried it?

I'm afraid that's about the best you can go with Go templates - there are sadly no "break" or "continue" operators to rely on.

--Michael

To view this discussion on the web visit https://groups.google.com/d/msgid/consul-tool/39fdd67c-3c38-43ca-bf3d-528c64806543%40googlegroups.com.

[DJ Enriquez]

Thanks Michael. I did try this and it will not work because setting $found inside {{range}} only changes the value within the scope of {{range}}. Once you exit out of {{range}}, $found goes right back to "no".

Here is a real example created by consul-template for a service I have called hello-world:

{{range services}}

  {{$found := "no"}}

  {{range service .Name}}

    {{if and (eq $found "no") (.Tags.Contains "lbc") (.Tags.Contains $app_env) (.Tags.Contains "ab")}}

    #{{.Name}} is "ab" and {{$app_env}}

    {{$found := "yes"}}

    {{end}}

  {{end}}

  {{if eq $found "no"}}

    #Did not find "ab" and {{ $app_env }}: {{.Name}}

  {{end}}

{{end}}

This template outputs:

    #hello-world is "ab" and dev

    #Did not find "ab" and dev: hello-world

As you can see, it found it, then it goes writes the case if $found = "no".