FAQ about remote connection of simple application servers - Simple Application Server

This topic provides the troubleshooting procedure for remote connection failures of simple application servers. This topic also provides answers to commonly asked questions about remote connection of simple application servers.

Troubleshooting procedure

If you cannot connect to a simple application server, we recommend that you troubleshoot the problem based on the following procedure. The troubleshooting procedure is sorted by the probability of the causes. We recommend that you troubleshoot the problem in sequence. This helps you quickly identify the cause of the problem. If the problem persists after you fix a possible cause, proceed to the next cause until the problem is solved.

Procedure	Operation
Check whether the server status is normal.	Only simple application servers that are in the Running state allow you to log on. If the status of the server is Stopped, restart the server. Warning The restart operation stops the instance for a short period of time and may interrupt services that are running on the instance. We recommend that you restart instances during off-peak hours. If the status of the server is Disabled, perform the following operations: Check whether the server is expired. If the server is expired, renew the server. For more information, see Upgrade and renew a simple application server. Check whether you have an overdue payment for the server. If you have an overdue payment for the server, add funds to the account. For information about how to view the status of a server, see View server information.
Check whether the logon credentials are valid.	Make sure that you use a valid username and password or use a valid key pair to log on to the server. If you forget the logon password, you can reset the password by using the password resetting feature. After you reset the password, restart the simple application server to allow the new password to take effect. For more information, see Set or reset the password of a server. If the key pair is invalid, change the key pair. For more information, see Change a key pair. If you use the Simple Application Server console to log on to the server but fail, submit a ticket to ask Alibaba Cloud to check whether the key file is unexpectedly deleted.
Check whether the port configurations are correct.	Check whether the logon port is enabled on the firewall. The default logon port is port 22 for Linux servers and port 3389 for Windows servers. If the corresponding port is not enabled, enable it. For more information, see Manage the firewall of a server.
Check whether the firewall is enabled.	If the server runs a Windows OS, disable the firewall.
Check whether the server is deployed outside the Chinese mainland.	If you are in the Chinese mainland and attempt to connect to a simple application server in a region outside the Chinese mainland, latency and packet loss may occur, which makes the server inaccessible. This is a problem with the Internet service providers and cannot be solved on the server. For more information, see What do I do if I am prompted that the connection has timed out when I connect to a simple application server deployed outside the Chinese mainland?
Check whether the network is stable	Use an on-premises host in another network environment to connect to the simple application server, or use another wireless network such as a mobile phone hotspot to test the access. This measure can help you find out whether the connection fails due to a local network problem. If the problem is not caused by the local network, perform further checks. If the local network causes the connection failure, we recommend that you contact the local network provider to solve the problem.
Check whether the server is overloaded.	If the utilization of the bandwidth or vCPUs of the simple application server is excessive, you may fail to log on to the server. To solve the problem, perform the following operations: Close processes that are not currently used and try again. Restart the simple application server. Reset the simple application server. Back up important data before you reset the server. For more information, see Reset a simple application server. Upgrade the server. For more information, see Upgrade a simple application server.
Check whether an antivirus software blocks the connection.	Third-party antivirus software may cause the failure of connection to the simple application server. If a third-party antivirus software is running, check whether the antivirus software blocks the connection to the simple application server. If the antivirus software blocks the connection, add the public IP address of the simple application server to the whitelist, and then retry the connection. You can also disable or uninstall the third-party antivirus software and try again.
Check whether the server is infected by viruses such as mining viruses.	If blackhole filtering is triggered for the public IP address of the simple application server due to attacks, you can manually deactivate blackhole filtering and try the connection again. For more information, see Blackhole filtering policy of Alibaba Cloud.
Check whether the Remote Desktop Protocol (RDP) of the server is enabled.	If the simple application server runs a Windows OS, check whether the RDP is enabled. If the RDP is disabled, enable it. For more information, see How do I troubleshoot the failure to connect to a Windows server while no error message appears?
Check the specific error message of the connection	Troubleshoot the problem based on the specific error message. For more information, see FAQ navigation.

If the problem persists after you take the preceding measures, submit a ticket to obtain technical support.

FAQ navigation

Common issues of connections
Failure to connect to a Linux server
- What do I do if the connection to a Linux server fails when SELinux is enabled on the Linux server?
- You can also use Elastic Compute Service (ECS) connection solutions to troubleshoot problems. For more information, see Failed to connect to the Linux instance.
Failure to connect to a Windows server

What do I do if I am prompted that the connection has timed out when I connect to a simple application server deployed outside the Chinese mainland?

If you are in the Chinese mainland and attempt to connect to a server deployed outside the Chinese mainland, latency and packet loss may occur, which causes the server to be inaccessible. This is a problem with the Internet service providers and cannot be solved on the server. For information about the regions where Simple Application Server is supported, see Regions and network connectivity. You can use one of the following methods to solve this problem:

If the network inaccessibility problem is not a consistent problem, you can change the local network environment or try to connect to the server later.
If your server is not required to be deployed outside the Chinese mainland, we recommend that you request a refund for your server and purchase a server deployed in the Chinese mainland.
Note
If you cannot request refunds for servers, submit a ticket.

How do I apply for unlocking the public IP address of the server?

If a server is locked due to infection by mining viruses or due to attacks, you can apply for unlocking the server. To apply for unlocking servers, go to the Penalties page of the Security Center console.

Note

For each server, you can apply for unlocking it only once.
A server that has been unlocked is automatically checked after 3 days. If a mining program is detected on the server again, the server is locked and cannot be unlocked.
After the server is unlocked, back up the data on the server at your earliest opportunity.

Why am I prompted that the connection is rejected when I fail to connect to my server?

This may be caused by one of the following issues. Fix the issue:

The remote service that corresponds to SSH or RDP is not enabled on the server.
Ports used for remote connections, such as SSH port 22 and RDP port 3389, are not enabled on the server.

Why am I prompted that the logon username or password is invalid when I fail to connect to the server?

This may be caused by one of the following issues. Fix the issue:

The username or password that you entered is invalid. The username is root for Linux servers and administrator for Windows servers.
The logon password that you entered is invalid. If you forget the logon password, you can reset the password. For more information, see Set or reset the password of a server.
If you log on to a Windows server as a non-administrator user, the user must belong to the Remote Desktop Users group.

Why does the error message "An error occurred. Try again later" appears when I connect to the simple application server by using Virtual Network Console (VNC) or the workbench?

When you connect to the simple application server on the server card, the error message "An error occurred. Try again later" appears. dasda To troubleshoot the issue, perform the following operations:

Connect to the server by using a third-party tool such as PuTTY.
Run the following command to check whether the SSH public key file authorized_keys exists:
```
cd /home/admin/.ssh/
ll
```
- If the SSH public key file does not exist, submit a ticket to obtain the SSH public key information, and restore the SSH public key file. Procedure:
  1. Run the following command to restore the SSH public key file:
```
mkdir -p /home/admin/.ssh
vim /home/admin/.ssh/authorized_keys
```
    Paste the public key information into the SSH public key file and save the file.
  2. Run the following command to change the file group:
```
chown -R admin:admin /home/admin
```
- If the SSH public key file authorized_keys exists, run the cat /home/admin/.ssh/authorized_keys command, copy the public key file information, and then submit a ticket that contains the public key file information to the technical support.
Check whether the /etc/sudoers file contains admin ALL=(ALL) NOPASSWD:ALL.
```
vim /etc/sudoers
```
If the /etc/sudoers file does not contain admin ALL=(ALL) NOPASSWD:ALL, add admin ALL=(ALL) NOPASSWD:ALL to the file.
Check whether the /home/admin/.ssh/authorized_keys file is granted the 644 permission.
```
cd /home/admin/.ssh
ll
```
The following command output is returned:
```
[root@iZd3ru25weg**** .ssh]# ll
total 0
-rw-r--r-- 1 admin admin 272 Nov  3 10:52 authorized_keys
```
If the file is not granted the 644 permission, run the chmod 644 authorized_keys command to grant the 644 permission.

What do I do if the connection to a Linux server fails when SELinux is enabled on the Linux server?

For information about how to solve the problem, see An SSH remote connection exception occurs in a Linux instance because the SELinux service is enabled.

If Security-Enhanced Linux (SELinux) is enabled, system security can be enhanced. However, after SELinux is enabled, the files of the operating system are damaged, and failures occur on system startup. We recommend that you enable or disable SELinux in an appropriate manner to prevent the system from failing to start up. For more information, see Enable or disable SELinux.

What do I do if an authentication problem occurs when I connect to a Windows server?

This problem may be caused by upgrade patches released by Windows. For information about how to solve the problem, seeThe error message "An authentication error has occurred. The function requested is not supported" appears when I connect to a simple application server. What do I do?

What do I do if I cannot connect to a Windows server by using the administrator account?

If you configure security policies on your Windows computer to deny logons from terminal services, you cannot use Remote Desktop Connection (RDC) on your Windows computer to connect to a Windows server by using the administrator account. For more information, see What do I do if the message "To sign in remotely, you need the right to sign in through Remote Desktop Services" appears when I connect to a Windows instance by using Remote Desktop?

How do I troubleshoot the failure to connect to a Windows server while no error message appears?

This problem occurs when you use the RDC tool on your Windows computer to connect to a Windows server. This may be because remote connection permissions are not enabled on the Windows server. In this example, Windows Server 2012 R2 64-bit is used to describe how to solve this problem.

Use the Simple Application Server console to connect to the Windows server.
For more information, see Connect to a Windows server.
Open This PC. In the left-side navigation pane, right-click This PC and select Properties.
In the left-side navigation pane of the System page, click Remote settings.
In the Remote Desktop section of the System Properties dialog box, select Allow remote connection to this computer.
Click Apply and then click OK.
After the configurations are complete, you can try to connect to the server again.

What do I do if the "The remote computer that you are trying to connect to requires Network Level Authentication (NLA)" message appears when I connect to a Windows server?

When you use the RDC tool on your Windows computer to connect to a Windows server, the message may be prompted. This may be because the RDC tool on your computer is of an earlier version. In this example, Windows Server 2012 R2 64-bit is used to describe how to solve this problem.

Use the Simple Application Server console to connect to the Windows server.
For more information, see Connect to a Windows server.
Open This PC. In the left-side navigation pane, right-click This PC and select Properties.
In the left-side navigation pane of the System page, click Remote settings.
In the Remote Desktop section of the System Properties dialog box, clear Allow connections only from computers running Remote Desktop with Network Level Authentication (recommended).
Click Apply and then click OK.
After the configurations are complete, you can try to connect to the server again.

What do I do if the "The remote session was disconnected because there are no Remote Desktop client access licenses available for this computer" message appears when I connect to a Windows server?

For information about how to solve the problem, see What do I do if the "The remote session was disconnected because there are no Remote Desktop client access licenses available for this computer" message appears when I connect to a Windows instance by using Remote Desktop?

What do I do if I cannot connect to a Windows server and the server has no Internet access capability?

A possible cause of this problem is that network interface controllers (NICs) are disabled on the Windows server. In this example, Windows Server 2012 R2 64-bit is used to describe how to solve this problem.

Use the Simple Application Server console to connect to the Windows server.
For more information, see Connect to a Windows server.
In the lower-right corner of the desktop, right-click the network icon and select Open Network and Sharing Center.
In the left-side navigation pane, click Change adapter settings.
Find the disabled network, right-click the network, and then select Enable.
After the network is enabled, right-click the network and select Properties.
In the This connection uses the following items section, click Internet Protocol Version 4 (TCP/IPv4) and click Properties.
On the General tab, click Obtain an IP address automatically, click Obtain DNS server address automatically, and then click OK.
After the configurations are complete, you can try to connect to the server again.