Allow checkFunction perform the entire check

[Gunni]

• Program: dnsdist
• Issue type: Feature request

Short description

I want to override how checkFunction works, for example, i want to fail a healthcheck if a specific domain does not return a REFUSED response.

Usecase

I have an adblocking backend, but if I exceed a quota, it starts working transparently, without blocking ads, i then want to mark that pool as "offline" and move on to the next pool.

function checkAdblocking(qname, qtype, qclass, dh)
        -- magic?
        return true
end

newServer({
        name="adblocker1",
        address="2001:db8::1",
        tls="openssl",
        subjectName="a.example.com",
        validateCertificates=true,
        pool="adblocker1",
        checkFunction=checkAdblocking
})

newServer({
        name="adblocker2",
        address="2001:db8::2",
        tls="openssl",
        subjectName="b.example.com",
        validateCertificates=true,
        pool="adblocker2",
        checkFunction=checkAdblocking
})

newServer({
        name="generic1",
        address="2001:db8::3",
        tls="openssl",
        subjectName="c.example.com",
        validateCertificates=true,
        pool="generic1"
})

-- I want these pools to be marked "down" if the query for
-- bad_domain.example.com starts responding anything other than REFUSED.
addAction(PoolAvailableRule("adblocker1"), PoolAction("adblocker1"))
addAction(PoolAvailableRule("adblocker2"), PoolAction("adblocker2"))

-- Fallback pool if all of the above are "down"
addAction(PoolAvailableRule("generic1"), PoolAction("generic1"))

-- All pools down?
addAction(AllRule(), RCodeAction(DNSRCode.REFUSED))

Description

Related discussion: #15055

Seems fairly straightforwards?

Modify checkFunction to allow boolean responses, and if boolean then use that as a result instead of a qname?

[rgacogne]

Hi! Thank you for filing this feature request!
We cannot modify the semantics of checkFunction without breaking existing configurations, which I would like to avoid, but we can take a new, optional function that takes information about the response and returns a boolean to indicate whether the response should be considered valid or not.

[rgacogne]

Setting the milestone to 2.1 since 2.0 is already well on its way and I don't think we will have the time to tackle this, but if someone is willing to contribute the code 2.0 might be doable.