Is it OK to generate session secret(or any other secret keys) and store it in host server?

I'm testing Google OAuth2.0 on node.js + express and using express-session for managing session, and I came across that I need Secret Key for my session manager.

So I did some research and found a post, which has some nice suggestions. But it seems to require some workarounds, like setting secret key as environment variable or keeping it in configuration file.

• Using the former, I need to enter environment variables every time I redeploy sever.
• Using the latter exposes my secret key to SCM.

So I decided to generate random string and store it in the host file system. It seems to solve all the problems I introduced above, but I'm noob to web development so I'm not sure whether this is legit.

Is there any cons or exploit to this method?

Below is my sessionSecret.js file:

var crypto = require('crypto');
var fs = require('fs');

var filePath = '/home/ubuntu/results.txt';

function readSecretKey() {
    return new Promise(function(resolve, reject) {
        fs.readFile(filePath, 'utf8', function(err, key) {
            if (err) {
                reject(err);
            } else {
                resolve(key);
            }
        });
    });
}

function writeSecretKey(key) {
    return new Promise(function(resolve, reject) {
        fs.writeFile(filePath, key, function(err) {
            if (err) {
                reject(err);
            } else {
                resolve(key);
            }
        }); 
    });
}

function generateRandomString() {
    return new Promise(function(resolve, reject) {
        crypto.randomBytes(48, function(err, buf) {
            if (err) {
                reject(err);
            } else {
                resolve(buf.toString('hex'));
            }
        })
    });
}

module.exports.getOrCreate = function() {
    return new Promise(function(resolve, reject) {
        readSecretKey()
            .then(function(key) {
                console.log("Key exists: " + key);
                resolve(key);
            }, function() {
                console.log("Key does not exists. Generating...");
                return generateRandomString();
            })
            .then(function(key) {
                if (key) {
                    console.log("Key generated: " + key);
                    return writeSecretKey(key);
                }
            }).then(function(key) {
                if (key) {
                    resolve(key);
                }
            }, function(err) {
                reject(err);
            });
    });
};