Maintaining a production big table
CREATE TABLE Table1_new LIKE Table1;
INSERT INTO Table1_new SELECT * FROM Table1;
ALERT TABLE Table1_new ADD COLUMN a;         --slow because of big table


is not optimal and has a problem.  Better:

CREATE TABLE Table1_new LIKE Table1;
ALERT TABLE Table1_new ADD COLUMN a;          -- fast because table empty
INSERT INTO Table1_new SELECT *, NULL FROM Table1; -- needs value for `a`


The problem is -- What if Table1 is being written to?  Such DML would be lost.

ALERT TABLE Table1 RENAME Table1_bu;
ALERT TABLE Table1_new RENAME Table1;


Should be done as a single statement (atomically):

RENAME TABLE Table1 TO Table1_bu,
             Table1_new TO Table1;


Plan A:  (Your code, after fixes):  Viable only if no modifications will happen.

Plan B:  pt-online-schema-change (assuming you have not Triggers on the table).

Plan C:  oak... -- No; it seems not tok be maintained

Plan D:  Upgrade to MySQL 8.0 (perhaps MariaDB 10.3) so you can get ALTER TABLE .. ADD COLUMN .. ALGORITHM=INSTANT