You can indeed in theory reuse the same CSR, as this is just a container for

- your Public Key (only
**Numbers** used for RSA encryption (specific maths) )
- your "Subject" details (who you are, what domain, etc ...)
**Text** used to Identify the owner of that Public Key

This is what a certificate (short for PublicKey Certificate) is about after all

But as noted in other answers, it is a good pratice to change private key regularly, so that implies new Certificate, and so new CSR to get it.

You can easily look at the contents of a CSR

e.g.

```
$ openssl req -new -batch -subj "/CN=My Common Name/OU=My Org Unit/O=My Organisation" -sha256 -newkey rsa:2048 -keyout private.key -nodes -out request.csr
Generating a 2048 bit RSA private key
.............................................................................................+++++
.........+++++
writing new private key to 'private.key'
-----
$ ls
private.key // keep that private, the PublicKey side is easily be generated from this
request.csr // your PublicKey + Subject details
```

CSR

```
$ openssl req -in request.csr -text -noout
Certificate Request:
Data:
Version: 1 (0x0)
Subject: CN = My Common Name, OU = My Org Unit, O = My Organisation
Subject Public Key Info:
Public Key Algorithm: rsaEncryption
RSA Public-Key: (2048 bit)
Modulus: ///////// Matches the PrivateKey modulus
00:b1:e8:de:e6:bf:21:45:51:75:15:23:5e:6e:7a:
7d:95:53:e5:d5:ec:5b:38:cd:7f:38:2d:53:8a:54:
...
fe:b5:78:de:9b:c1:ee:c1:51:6f:fd:fb:0e:62:09:
03:87
Exponent: 65537 (0x10001) ///////// Matches the PrivateKey publicExponent
Attributes:
a0:00
Signature Algorithm: sha256WithRSAEncryption
a1:44:1f:b2:ec:c0:82:bc:99:da:69:ce:3e:77:9f:46:51:95:
...
3b:2d:84:e3:73:ac:be:c8:da:29:fd:62:90:11:dd:8a:a6:4f:
7b:f8:ac:f1
```

And PrivateKey

```
$ openssl rsa -in private.key -text -noout
// all the below are numbers that takes part in Mathematical encryption (search for RSA maths)
RSA Private-Key: (2048 bit, 2 primes)
// The Numbers that can be freely published
modulus:
00:b1:e8:de:e6:bf:21:45:51:75:15:23:5e:6e:7a:
7d:95:53:e5:d5:ec:5b:38:cd:7f:38:2d:53:8a:54:
...
fe:b5:78:de:9b:c1:ee:c1:51:6f:fd:fb:0e:62:09:
03:87
publicExponent: 65537 (0x10001)
// The Numbers that must be kept private !
privateExponent:
0a:81:73:d8:30:65:28:90:bc:d7:38:b5:74:d4:aa:
...
b1:9b:30:2e:a2:dd:46:c1:10:0f:b0:da:ac:b6:ea:
01
prime1:
00:e0:28:01:87:95:70:d0:b8:21:07:e0:4f:96:a6:
...
66:28:8f:3d:d7:eb:e6:b4:81
prime2:
00:cb:2e:fe:1b:b6:30:ea:8d:9e:6d:23:83:d8:b6:
...
4d:64:39:5c:9c:18:a0:14:07
exponent1:
22:e2:36:f2:b9:af:f7:db:5f:d0:90:f8:f1:d1:ff:
...
3a:31:a8:87:2c:c0:17:81
exponent2:
5a:8b:3d:77:f1:ef:c8:86:85:a4:13:20:8d:31:a4:
...
a5:ba:1e:37:fd:8d:50:7f
coefficient:
00:d3:d3:b6:81:4b:a9:c2:aa:ff:e1:07:cb:de:ea:
...
5c:e9:3b:d3:f7:67:82:c3:7f
```