如何排查Node.js中TLS握手缓慢的问题？

近期系统新增大量用户，带宽使用及TLS握手后的服务器响应均处于正常范围，但TLS握手耗时可达1-2.5秒，其中客户端问候（Client Hello）与服务器问候（Server Hello）之间的延迟尤为明显，以下是耗时1.5秒的日志片段：

13:01:49.599739 * TLSv1.3 (OUT), TLS handshake, Client hello (1):
13:01:51.023274 * TLSv1.3 (IN), TLS handshake, Server hello (2):

我们的运行环境是Node.js 16搭配greenlock-express，个人认为express或greenlock与握手延迟无关。

发现重启pm2进程后，握手速度会暂时恢复正常，日志如下：

13:20:24.977793 * TLSv1.3 (OUT), TLS handshake, Client hello (1):
13:20:25.063494 * TLSv1.3 (IN), TLS handshake, Server hello (2):

除了Client Hello到Server Hello之间的延迟，整体请求日志的其他环节均运行顺畅，完整curl请求日志如下：

:~$ curl -iv  --trace-time https://{server name}
13:01:49.496453 * Rebuilt URL to: https://{server name}/
13:01:49.500927 *   Trying 54.73.36.16...
13:01:49.500970 * TCP_NODELAY set
13:01:49.583976 * Connected to {server name} (54.73.36.16) port 443 (#0)
13:01:49.585712 * ALPN, offering h2
13:01:49.585791 * ALPN, offering http/1.1
13:01:49.599251 * successfully set certificate verify locations:
13:01:49.599324 *   CAfile: /etc/ssl/certs/ca-certificates.crt
  CApath: /etc/ssl/certs
13:01:49.599739 * TLSv1.3 (OUT), TLS handshake, Client hello (1):
13:01:51.023274 * TLSv1.3 (IN), TLS handshake, Server hello (2):
13:01:51.023566 * TLSv1.3 (IN), TLS Unknown, Certificate Status (22):
13:01:51.023602 * TLSv1.3 (IN), TLS handshake, Unknown (8):
13:01:51.023679 * TLSv1.3 (IN), TLS Unknown, Certificate Status (22):
13:01:51.023764 * TLSv1.3 (IN), TLS handshake, Certificate (11):
13:01:51.024257 * TLSv1.3 (IN), TLS Unknown, Certificate Status (22):
13:01:51.024312 * TLSv1.3 (IN), TLS handshake, CERT verify (15):
13:01:51.024439 * TLSv1.3 (IN), TLS Unknown, Certificate Status (22):
13:01:51.024504 * TLSv1.3 (IN), TLS handshake, Finished (20):
13:01:51.024599 * TLSv1.3 (OUT), TLS change cipher, Client hello (1):
13:01:51.024708 * TLSv1.3 (OUT), TLS Unknown, Certificate Status (22):
13:01:51.024785 * TLSv1.3 (OUT), TLS handshake, Finished (20):
13:01:51.024902 * SSL connection using TLSv1.3 / TLS_AES_256_GCM_SHA384
13:01:51.024957 * ALPN, server accepted to use http/1.1
13:01:51.025023 * Server certificate:
13:01:51.025089 *  subject: CN={server name}
13:01:51.025143 *  start date: Oct 10 07:55:03 2022 GMT
13:01:51.025205 *  expire date: Jan  8 07:55:02 2023 GMT
13:01:51.025273 *  subjectAltName: host "{server name}" matched cert's "{server name}"
13:01:51.025341 *  issuer: C=US; O=Let's Encrypt; CN=R3
13:01:51.025402 *  SSL certificate verify ok.
13:01:51.025490 * TLSv1.3 (OUT), TLS Unknown, Unknown (23):
13:01:51.025584 > GET / HTTP/1.1
13:01:51.025584 > Host: {server name}
13:01:51.025584 > User-Agent: curl/7.58.0
13:01:51.025584 > Accept: */*
13:01:51.025584 >
13:01:51.139620 * TLSv1.3 (IN), TLS Unknown, Certificate Status (22):
13:01:51.139776 * TLSv1.3 (IN), TLS handshake, Newsession Ticket (4):
13:01:51.139981 * TLSv1.3 (IN), TLS Unknown, Certificate Status (22):
13:01:51.140130 * TLSv1.3 (IN), TLS handshake, Newsession Ticket (4):
13:01:51.221629 * TLSv1.3 (IN), TLS Unknown, Unknown (23):
13:01:51.221752 < HTTP/1.1 200 OK
HTTP/1.1 200 OK
13:01:51.221934 < X-Powered-By: Express
X-Powered-By: Express
13:01:51.222112 < Vary: Origin
Vary: Origin
13:01:51.222265 < Accept-Ranges: bytes
Accept-Ranges: bytes
13:01:51.222428 < Cache-Control: public, max-age=0
Cache-Control: public, max-age=0
13:01:51.222564 < Last-Modified: Sun, 13 Nov 2022 13:14:39 GMT
Last-Modified: Sun, 13 Nov 2022 13:14:39 GMT
13:01:51.222687 < ETag: W/"403-1847120b218"
ETag: W/"403-1847120b218"
13:01:51.222811 < Content-Type: text/html; charset=UTF-8
Content-Type: text/html; charset=UTF-8
13:01:51.222946 < Content-Length: 1027
Content-Length: 1027
13:01:51.223068 < Set-Cookie: connect.sid=s%3AD0KBzxmVDIb8vYcBmtdTZ6bvRF17NT1Q.1c6pkFHEoNWHl%2F4OT6bqMkm1csE; Path=/; HttpOnly
Set-Cookie: connect.sid=s%3AD0KBzxmVDIb8vYcBmtdTZ6bvRF17NT1Q.1c6pkFHEoNWbqMkm1csE; Path=/; HttpOnly
13:01:51.223192 < Date: Tue, 22 Nov 2022 11:01:50 GMT
Date: Tue, 22 Nov 2022 11:01:50 GMT
13:01:51.223316 < Connection: keep-alive
Connection: keep-alive
13:01:51.223439 < Keep-Alive: timeout=5
Keep-Alive: timeout=5

13:01:51.223567 <
<!doctype html>

请问该如何定位TLS握手缓慢的原因？

内容的提问来源于stack exchange，提问作者Hillel Millman