server.js

// Require the framework and instantiate it
const fastify = require('fastify')();
const mjml = require('mjml');

process.on('SIGINT', function() {
    process.exit();
});

fastify.post('/render', { bodyLimit: 10485760 }, function (request, reply) {
    try {
        let template = request.body.files[request.body.template];

        let rendered;
        try {
            rendered = mjml(template).html;
        } catch (e) {
            console.log(e);
            reply
                .code(400)
                .type('application/problem+json')
                .send(
                    JSON.stringify(
                        {
                            title: "MJML Error",
                            detail: e.message
                        }
                    )
                );
            return;
        }

        reply
            .code(200)
            .type('text/html')
            .send(rendered);

    } catch (e) {
        console.log(e);
        reply
            .code(500)
            .type('application/problem+json')
            .send(
                JSON.stringify(
                    {
                        title: "Server Error"
                        // detail: e.message
                    }
                )
            );

    }
});

// Run the server!
fastify.listen(80, '0.0.0.0', function (err) {
    if (err) throw err;
    console.log(`server listening on ${fastify.server.address().port}`)
});