diff --git a/service/user/internal/src/main/java/org/eclipse/kapua/service/user/internal/UserServiceImpl.java b/service/user/internal/src/main/java/org/eclipse/kapua/service/user/internal/UserServiceImpl.java
index 7209b2c232e..eeb199ba5ea 100644
--- a/service/user/internal/src/main/java/org/eclipse/kapua/service/user/internal/UserServiceImpl.java
+++ b/service/user/internal/src/main/java/org/eclipse/kapua/service/user/internal/UserServiceImpl.java
@@ -89,6 +89,7 @@ public User create(UserCreator userCreator) throws KapuaException {
         ArgumentValidator.notNull(userCreator.getScopeId().getId(), "userCreator.scopeId");
         ArgumentValidator.notEmptyOrNull(userCreator.getName(), "userCreator.name");
         ArgumentValidator.match(userCreator.getName(), CommonsValidationRegex.NAME_REGEXP, "userCreator.name");
+        ArgumentValidator.lengthRange(userCreator.getName(), 3, 255, "userCreator.name");
         ArgumentValidator.match(userCreator.getEmail(), CommonsValidationRegex.EMAIL_REGEXP, "userCreator.email");
         ArgumentValidator.notNull(userCreator.getStatus(), "userCreator.status");
 
@@ -96,8 +97,10 @@ public User create(UserCreator userCreator) throws KapuaException {
         if (userCreator.getUserType() == UserType.EXTERNAL) {
             if (userCreator.getExternalId() != null) {
                 ArgumentValidator.notEmptyOrNull(userCreator.getExternalId(), "userCreator.externalId");
+                ArgumentValidator.lengthRange(userCreator.getExternalId(), 3, 255, "userCreator.externalId");
             } else {
                 ArgumentValidator.notEmptyOrNull(userCreator.getExternalUsername(), "userCreator.externalUsername");
+                ArgumentValidator.lengthRange(userCreator.getExternalUsername(), 3, 255, "userCreator.externalUsername");
             }
         } else if (userCreator.getUserType() == UserType.INTERNAL) {
             ArgumentValidator.isEmptyOrNull(userCreator.getExternalId(), "userCreator.externalId");
@@ -159,6 +162,7 @@ public User update(User user) throws KapuaException {
         ArgumentValidator.notNull(user.getScopeId(), "user.scopeId");
         ArgumentValidator.notEmptyOrNull(user.getName(), "user.name");
         ArgumentValidator.match(user.getName(), CommonsValidationRegex.NAME_REGEXP, "user.name");
+        ArgumentValidator.lengthRange(user.getExternalId(), 3, 255, "user.name");
         ArgumentValidator.match(user.getEmail(), CommonsValidationRegex.EMAIL_REGEXP, "user.email");
         ArgumentValidator.notNull(user.getStatus(), "user.status");
         ArgumentValidator.notNull(user.getUserType(), "user.userType");
@@ -166,8 +170,10 @@ public User update(User user) throws KapuaException {
         if (user.getUserType() == UserType.EXTERNAL) {
             if (user.getExternalId() != null) {
                 ArgumentValidator.notEmptyOrNull(user.getExternalId(), "user.externalId");
+                ArgumentValidator.lengthRange(user.getExternalId(), 3, 255, "user.externalId");
             } else {
                 ArgumentValidator.notEmptyOrNull(user.getExternalUsername(), "user.externalUsername");
+                ArgumentValidator.lengthRange(user.getExternalUsername(), 3, 255, "user.externalUsername");
             }
         } else if (user.getUserType() == UserType.INTERNAL) {
             ArgumentValidator.isEmptyOrNull(user.getExternalId(), "user.externalId");
diff --git a/service/user/internal/src/main/resources/liquibase/2.0.0/user-external_username.xml b/service/user/internal/src/main/resources/liquibase/2.0.0/user-external_username.xml
index 78d3f9375ed..e1fa6b1274e 100644
--- a/service/user/internal/src/main/resources/liquibase/2.0.0/user-external_username.xml
+++ b/service/user/internal/src/main/resources/liquibase/2.0.0/user-external_username.xml
@@ -18,12 +18,46 @@
                       http://www.liquibase.org/xml/ns/dbchangelog/dbchangelog-3.0.xsd"
         logicalFilePath="KapuaDB/changelog-user-2.0.0.xml">
 
-    <changeSet id="changelog-user_2.0.0_external-username" author="eurotech">
+    <!--  This has been commented since UNIQUE creates an index on the field, which makes this column creation incompatible  -->
+    <!--  with MySQL/MariaDB databases that have a length limit of 767 bytes per index. -->
+    <!--  Index will be redefined as NOT UNIQUE with an index on the column to improve query performances  -->
+    <!--    -->
+    <!--    <changeSet id="changelog-user_2.0.0_external-username" author="eurotech">-->
+    <!--        <addColumn tableName="usr_user">-->
+    <!--            <column name="external_username" type="varchar(1024)">-->
+    <!--                <constraints unique="true"/>-->
+    <!--            </column>-->
+    <!--        </addColumn>-->
+    <!--    </changeSet>-->
+
+    <changeSet id="changelog-user_2.0.0_external-username-fix-create" author="eurotech">
+        <preConditions onFail="MARK_RAN">
+            <not>
+                <columnExists tableName="usr_user" columnName="external_username"/>
+            </not>
+        </preConditions>
+
         <addColumn tableName="usr_user">
-            <column name="external_username" type="varchar(1024)">
-                <constraints unique="true"/>
-            </column>
+            <column name="external_username" type="varchar(255)"/>
         </addColumn>
     </changeSet>
+    <changeSet id="changelog-user_2.0.0_external-username-fix-modify" author="eurotech">
+        <preConditions onFail="MARK_RAN">
+            <columnExists tableName="usr_user" columnName="external_username"/>
+        </preConditions>
+
+        <modifyDataType tableName="usr_user" columnName="external_username" newDataType="varchar(255)"/>
+    </changeSet>
+
+    <changeSet id="changelog-user_2.0.0_external-username-fix-index" author="eurotech">
+        <preConditions onFail="MARK_RAN">
+            <not>
+                <indexExists tableName="usr_user" indexName="idx_externalUsername"/>
+            </not>
+        </preConditions>
 
+        <createIndex tableName="usr_user" indexName="idx_externalUsername">
+            <column name="external_username"/>
+        </createIndex>
+    </changeSet>
 </databaseChangeLog>