Ability to Use Prepared Query in Place of Service

[selble]

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Consul Template version

consul-template v0.18.5 (9902dd5)

Configuration

N/A

upstream exampleservice {
    least_conn;
    keepalive 16;

    #Attempt to fetch the exampleservice servers
    {{if service "exampleservice"}}
        {{range service "exampleservice"}}server {{.Address}}:8443;
    {{end}}
    {{else}} # upstream stanza must have a server directive
        server 127.0.0.1 down;
    {{end}}
}

Command

consul-template --template=/etc/templates/etc/nginx/virtual-servers/pws.conf:/etc/nginx/virtual-servers/pws.conf:systemctl reload nginx --template=/etc/templates/etc/nginx/locations/pws.conf:/etc/nginx/locations/pws.conf:systemctl reload nginx --template=/etc/templates/etc/nginx/upstreams/pws.conf:/etc/nginx/upstreams/pws.conf:systemctl reload nginx --wait=5s:10s

Debug output

N/A

Expected behavior

This is a feature request, so what I'd like to be able to do is something like this:

upstream exampleservice {
    least_conn;
    keepalive 16;

    #Attempt to fetch the exampleservice servers
    {{if query "exampleservice"}}
        {{range query "exampleservice"}}server {{.Address}}:8443;
    {{end}}
    {{else}} # upstream stanza must have a server directive
        server 127.0.0.1 down;
    {{end}}
}

Actual behavior

In the absence of using prepared queries, we are constrained to only having services within a given datacenter with the configuration as it exists. We could define a second section, with a hard coded backup:

upstream exampleservice {
    least_conn;
    keepalive 16;

    #Attempt to fetch the exampleservice servers
    {{if service "exampleservice"}}
        {{range service "exampleservice"}}server {{.Address}}:8443;
    {{end}}
    {{else}} # upstream stanza must have a server directive
        server 127.0.0.1 down;
    {{end}}

    #Attempt to fetch the backup exampleservice servers
    {{if service "exampleservice@guse4-poc"}}
        {{range service "exampleservice@guse4-poc"}}server {{.Address}}:8443 backup;
    {{end}}
    {{else}} # upstream stanza must have a server directive
        server 127.0.0.1 down;
    {{end}}
}

But that gets tricky to maintain, and query seems like the perfect solution for this, if it were an option to iterate over, as service is.

Steps to reproduce

N/A

References

Are there any other GitHub issues (open or closed) that should
be linked here? For example:
N/A