add support for fastify@4

Currently fastify v4 has RC pre-releases. Our TAV tests and supported-technologies doc page say we support fastify >=1. We should change that to be specific about the major versions support, and we should test and update for fastify v4 as necessary.

[trentm]

fastify@4 requires node >=14.6.0 – because it uses pino@8 which uses on-exit-leak-free@1 which requires https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/FinalizationRegistry which came in node 14.6.0.

[trentm]

@karliell

When I run this:

const fastify = require('fastify')
const app = fastify()
app.get('/ping', (req, reply) => {
    reply.send('pong')
})
app.listen({ port: 3000 }, (err) => { if (err) throw err }, () => {
    console.log("running on port 3000");
});

I see that FSTDEP011 warning:

(node:73658) [FSTDEP011] FastifyDeprecation: Variadic listen method is deprecated. Please use ".listen(optionsObject)" instead. The variadic signature will be removed in `fastify@5`.

However, when I run this:

const fastify = require('fastify')
const app = fastify()
app.get('/ping', (req, reply) => {
    reply.send('pong')
})
app.listen({port: 3000}, () => {
    console.log("running on port 3000");
});

I do not see that deprecation warning. I get the same behaviour whether or not the elastic-apm-node APM agent is being used.

Do you see different behaviour? I’m using fastify@4.9.2 and elastic-apm-node@3.40.1.