Add Resource tag into Context, for example^

 <Resource name="jdbc/PostgreDS" auth="Container"
    type="javax.sql.DataSource" driverClassName="org.postgresql.Driver"
    url="jdbc:postgresql://127.0.0.1:5432/schema"
    username="schema" password="1234" maxActive="50" maxIdle="10" maxWait="-1"/>

 <Resource name="jdbc/MysqlDS" auth="Container"
    type="javax.sql.DataSource" driverClassName="com.mysql.jdbc.Driver"
    url="jdbc:mysql://localhost:3306/schema"
    username="user" password="1234" maxActive="50" maxIdle="10" maxWait="-1"/>