Mysql setting constraints

https://www.percona.com/blog/2017/04/06/dealing-mysql-error-code-1215-cannot-add-foreign-key-constraint

  CONSTRAINT education_ibfk_1
    FOREIGN KEY (profile_id)
    REFERENCES Profile (profile_id)
    ON DELETE CASCADE ON UPDATE CASCADE,
  CONSTRAINT education_ibfk_2
    FOREIGN KEY (institution_id)
    REFERENCES Institution (institution_id)
    ON DELETE CASCADE ON UPDATE CASCADE,
 
 
 
 
CREATE TABLE sslhosts (
hostname VARCHAR(30) NOT NULL,
port INT(11) DEFAULT 443,
PRIMARY KEY (hostname)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
 
 
 
CREATE TABLE notes
(
hostname VARCHAR(30),
notes VARCHAR(100),
CONSTRAINT myconst_1
FOREIGN KEY (hostname)
REFERENCES sslhosts (hostname)
ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

http://www.mysqltutorial.org/mysql-primary-key/