ssh connect do not use identity from config - ssh

Question

I am trying to setup ssh connection to gitlab.com. I have corresponding identity file and it works if I use it explicitly. But failed when I expect it read identity file from config.
Here explicit usage:
ssh -v -i /root/.ssh/reshop-deploy -T git#gitlab.com
OpenSSH_7.4p1, OpenSSL 1.0.2k 26 Jan 2017
debug1: Reading configuration data /root/.ssh/config
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 1: Applying options for *
debug1: Connecting to gitlab.com [52.167.219.168] port 22.
debug1: Connection established.
debug1: permanently_set_uid: 0/0
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/reshop-deploy type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/reshop-deploy-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_7.4
debug1: Remote protocol version 2.0, remote software version OpenSSH_7.2p2 Ubuntu-4ubuntu2.1
debug1: match: OpenSSH_7.2p2 Ubuntu-4ubuntu2.1 pat OpenSSH* compat 0x04000000
debug1: Authenticating to gitlab.com:22 as 'git'
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: algorithm: curve25519-sha256#libssh.org
debug1: kex: host key algorithm: ecdsa-sha2-nistp256
debug1: kex: server->client cipher: chacha20-poly1305#openssh.com MAC: <implicit> compression: none
debug1: kex: client->server cipher: chacha20-poly1305#openssh.com MAC: <implicit> compression: none
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug1: Server host key: ecdsa-sha2-nistp256 SHA256:HbW3g8zUjNSksFbqTiUWPWg2Bq1x8xdGUrliXFzSnUw
debug1: Host 'gitlab.com' is known and matches the ECDSA host key.
debug1: Found key in /root/.ssh/known_hosts:36
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_EXT_INFO received
debug1: kex_input_ext_info: server-sig-algs=<rsa-sha2-256,rsa-sha2-512>
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey
debug1: Next authentication method: publickey
debug1: Trying private key: /root/.ssh/reshop-deploy
debug1: Authentication succeeded (publickey).
Authenticated to gitlab.com ([52.167.219.168]:22).
debug1: channel 0: new [client-session]
debug1: Requesting no-more-sessions#openssh.com
debug1: Entering interactive session.
debug1: pledge: network
debug1: client_input_global_request: rtype hostkeys-00#openssh.com want_reply 0
debug1: Remote: Forced command.
debug1: Remote: Port forwarding disabled.
debug1: Remote: X11 forwarding disabled.
debug1: Remote: Agent forwarding disabled.
debug1: Remote: PTY allocation disabled.
Welcome to GitLab, XXXX!
debug1: client_input_channel_req: channel 0 rtype exit-status reply 0
debug1: client_input_channel_req: channel 0 rtype eow#openssh.com reply 0
debug1: channel 0: free: client-session, nchannels 1
Transferred: sent 2880, received 2776 bytes, in 0.4 seconds
Bytes per second: sent 6778.9, received 6534.1
debug1: Exit status 0
But if I run it with hope on /root/.ssh/config I got:
ssh -v -T git#gitlab.com
OpenSSH_7.4p1, OpenSSL 1.0.2k 26 Jan 2017
debug1: Reading configuration data /root/.ssh/config
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 1: Applying options for *
debug1: Connecting to gitlab.com [52.167.219.168] port 22.
debug1: Connection established.
debug1: permanently_set_uid: 0/0
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_rsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_rsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_dsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_dsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_ecdsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_ecdsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_ed25519 type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_ed25519-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_7.4
debug1: Remote protocol version 2.0, remote software version OpenSSH_7.2p2 Ubuntu-4ubuntu2.1
debug1: match: OpenSSH_7.2p2 Ubuntu-4ubuntu2.1 pat OpenSSH* compat 0x04000000
debug1: Authenticating to gitlab.com:22 as 'git'
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: algorithm: curve25519-sha256#libssh.org
debug1: kex: host key algorithm: ecdsa-sha2-nistp256
debug1: kex: server->client cipher: chacha20-poly1305#openssh.com MAC: <implicit> compression: none
debug1: kex: client->server cipher: chacha20-poly1305#openssh.com MAC: <implicit> compression: none
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug1: Server host key: ecdsa-sha2-nistp256 SHA256:HbW3g8zUjNSksFbqTiUWPWg2Bq1x8xdGUrliXFzSnUw
debug1: Host 'gitlab.com' is known and matches the ECDSA host key.
debug1: Found key in /root/.ssh/known_hosts:36
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_EXT_INFO received
debug1: kex_input_ext_info: server-sig-algs=<rsa-sha2-256,rsa-sha2-512>
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey
debug1: Next authentication method: publickey
debug1: Trying private key: /root/.ssh/id_rsa
debug1: Authentications that can continue: publickey
debug1: Trying private key: /root/.ssh/id_dsa
debug1: Trying private key: /root/.ssh/id_ecdsa
debug1: Trying private key: /root/.ssh/id_ed25519
debug1: No more authentication methods to try.
Permission denied (publickey).
.ssh folder list:
ls -al /root/.ssh/
total 60
drwxr-x--- 2 root root 4096 Apr 25 17:54 .
drwx------ 11 root root 4096 Apr 25 18:01 ..
-rw------- 1 root root 5024 Jun 13 2016 authorized_keys
-rw------- 1 root root 193 Apr 25 17:48 config
-rw------- 1 root root 1675 Dec 4 2015 id_rsa
-rw-r--r-- 1 root root 13991 Apr 25 16:59 known_hosts
-rw------- 1 root root 3243 Apr 25 14:40 reshop-deploy
Here it is config content:
cat /root/.ssh/config
Host gitlab
Hostname gitlab.com
User git
IdentityFile ~/.ssh/reshop-deploy
IdentitiesOnly yes
Seems it ignores Identity file, but I don't understand why.

Answer 1

Your ~/.ssh/config configuration begins with Host gitlab. That means that all of the configuration directives after it, up to the next Host line, will only take effect if you refer to the server exactly as "gitlab" on the command line, e.g., ssh gitlab. If you also want your configuration to apply when doing ssh gitlab.com or ssh git#gitlab.com, then you need to change your Host line to Host gitlab gitlab.com.