After renew of certificate will it effect the backend node js operation any difference after Renew of the ssl certificate
A valid cert is a valid cert.
So switching from one valid cert (that is almost expired) to another valid cert (that has 90 days left) is routine.
It might "affect it" in the sense that if you are serving TLS directly from Node.js (i.e. using https://nodejs.org/api/https.html), then you will need to programmatically read the renewed certificate off the filesystem and call the right API (probably this one) to apply it.
For this reason, it is usually preferable to use a reverse proxy like nginx in front of Node.js, and allow nginx to deal with SSL certificates.
That way, you can reload nginx to your heart's content and the backend does not need to worry about SSL.
If I wanted the same certificate for More than 1 year what should I do?
then you have to buy a certificate from another CA.
Please read some basics:
Letsencrypt certificates are 90 days valid.
How to get more than a year the valid certificate, please any one can provide me with link so that i can visit the link to renew it
Thanks & Regards
You do what Juergen said and use a different CA. Certs from Let's Encrypt are valid for only 90 days. Renewals are free, so you can keep using them indefinitely, but it isn't possible to get a single cert from Let's Encrypt that's valid for more than 90 days. If you don't know what other certificate authority to try, do a web search for "certificate authority" and I'm sure you'll find several options.