VIP 17: Enable Unix domain sockets for listen and backend addresses

Synopsis

Allow Unix Domain Sockets (UDS) as listen addresses for Varnish (-a option) and as addresses for backends. Ideally also obtain credentials of the peer process connected on a UDS, such as uid and gid, for use in VCL.

Named listen addresses

This is not directly related to UDS, but this change would solve some of the problems and mitigate some the complexity raised by the original draft. Because this change has already been accepted, there is no VIP to link to, and no documentation to refer to until it is implemented. For convenience it is described here.

Influence

This feature is similar to how storage backends are exposed in VCL, they have a name that can then be used in VCL, and when a name is omitted, generic names are attributed (s0, s1, sN etc).

Example: varnishd -s malloc,10G -s video=malloc,100G [...]

You end up with 3 storage backends called s0, video and Transient, and as such have access in VCL to the following symbols and their respective fields:

• storage.s0
• storage.video
• storage.Transient
• (and storage.<name>.*, see man vcl)

You can then have this kind of logic in VCL:

sub vcl_backend_response {
    if (beresp.http.content-type ~ "video") {
        set beresp.storage = storage.video;
    } else {
        set beresp.storage = storage.s0;
    }
}

The advantage of beresp.storage over beresp.storage_hint is the strong typing guaranteeing that VCL won't compile if there is a typo in the storage name.

Implementation

Named listen addresses will work like storage backends in that regard (generic names being a0, a1, aN etc).

Example: varnishd -a public_http=:80 -a public_https=:8443,PROXY admin=:1234 [...]

You can then use the logical names in your VCL:

sub vcl_recv {
    if (local.address == listen_address.public_http) {
        # do an https redirect for example
    }
    if (req.method == "PURGE") {
        if (local.address != listen_address.admin) {
            return (synth(405));
        }
        return (purge);
    }
}

Actual names of the variables used to access this information in VCL hasn't been decided yet.

The benefits are the ability to reuse the same VCL when all varnishd instances in a cluster may not be able to provide consistent listen interfaces or port numbers.

Security concerns

This is not a security feature despite what the example above may suggest. Using this as a security measures implies the assumption that the network is actually secured before traffic hits Varnish on the admin listen address for example (firewalls and all that jazz).

Benefits

Once again strong typing, because port numbers in VCL and in the varnishd command line may get out of sync without being noticed. Here a typo in the name prevents the VCL from compiling. It's also a transport-independent alternative to ACLs, as shown in the purge example above.

Being transport-independent, it also means that it can accommodate future transports, like for example unix domain sockets described below.

Why?

TODO

How?

TODO