from within a project container,
$ curl -v https://anildash.com/ * Trying 220.127.116.11... * Connected to anildash.com (18.104.22.168) port 443 (#0) * found 148 certificates in /etc/ssl/certs/ca-certificates.crt * found 594 certificates in /etc/ssl/certs * ALPN, offering http/1.1 * SSL connection using TLS1.2 / ECDHE_ECDSA_AES_128_GCM_SHA256 * server certificate verification failed. CAfile: /etc/ssl/certs/ca-certificates.crt CRLfile: none * Closing connection 0 curl: (60) server certificate verification failed. CAfile: /etc/ssl/certs/ca-certificates.crt CRLfile: none More details here: http://curl.haxx.se/docs/sslcerts.html curl performs SSL certificate verification by default, using a "bundle" of Certificate Authority (CA) public keys (CA certs). If the default bundle file isn't adequate, you can specify an alternate file using the --cacert option. If this HTTPS server uses a certificate signed by a CA represented in the bundle, the certificate verification probably failed due to a problem with the certificate (it might be expired, or the name might not match the domain name in the URL). If you'd like to turn off curl's verification of the certificate, use the -k (or --insecure) option.
$ openssl s_client -connect anildash.com:443 -servername anildash.com </dev/null CONNECTED(00000003) depth=3 O = Digital Signature Trust Co., CN = DST Root CA X3 verify error:num=10:certificate has expired notAfter=Sep 30 14:01:15 2021 GMT --- Certificate chain 0 s:/CN=anildash.com i:/C=US/O=Let's Encrypt/CN=R3 1 s:/C=US/O=Let's Encrypt/CN=R3 i:/C=US/O=Internet Security Research Group/CN=ISRG Root X1 2 s:/C=US/O=Internet Security Research Group/CN=ISRG Root X1 i:/O=Digital Signature Trust Co./CN=DST Root CA X3 ---