I was working with different VM's testing the connection establishment times. One thing we noticed was that curl needed much longer to connect on some of the vm's than on others (3x as much or + 100ms). Upon checking the versions of the libraries we noticed that those ones performing bad were build against GnuTLS (3.4.10) while those ones performing good where build against OpenSSL.

Now this solved the problem for me but did want to report it somewhere in case someone has the same problem.

Not sure if this is a problem with curl in combination with GnuTLS or if OpenSSL just outperforms GnuTLS or something different.

 

For reference here are the different versions we tested and their connect times:

 

curl -V
curl 7.47.0 (x86_64-pc-linux-gnu) libcurl/7.47.0 GnuTLS/3.4.10 zlib/1.2.8 libidn/1.32 librtmp/2.3
Protocols: dict file ftp ftps gopher http https imap imaps ldap ldaps pop3 pop3s rtmp rtsp smb smbs smtp smtps telnet tftp
Features: AsynchDNS IDN IPv6 Largefile GSS-API Kerberos SPNEGO NTLM NTLM_WB SSL libz TLS-SRP UnixSockets

 

curl -o /dev/null -s -w '%{time_appconnect}\n' https://www.youtube.com
0.150

 

 

 

curl -V
curl 7.35.0 (x86_64-pc-linux-gnu) libcurl/7.35.0 OpenSSL/1.0.1f
zlib/1.2.8 libidn/1.28 librtmp/2.3
Protocols: dict file ftp ftps gopher http https imap imaps ldap ldaps
pop3 pop3s rtmp rtsp smtp smtps telnet tftp
Features: AsynchDNS GSS-Negotiate IDN IPv6 Largefile NTLM NTLM_WB SSL
libz TLS-SRP

 

curl -o /dev/null -s -w '%{time_appconnect}\n' https://www.youtube.com

Results where < 0.050

 

-- Bernhard Jaeger