The latest releases of Oracle Analytics Cloud (OAC) now include the new Remote Data Gateway (RDG) for accessing databases that are not otherwise accessible by OAC.
This post is a step-by-step guide to configuring an SSH Client to reach an RDG host (app-server) in a private subnet via a bastion host in a public subnet. For VPN / FastConnect users, it may be helpful but the bastion is not necessary.
This post is one of the strategies noted in the companion blog Deploying Oracle Analytics Cloud Remote Data Gateway in a Private Subnet
March 17, 2020 for Linux 7.7 and MacOS 10.13.6
MacBook Pro OS 10.13.6
SSH Client (MacOS) OpenSSH_7.8p1
SSH Server (Linux) OpenSSH_7.4p1
Bitvise SSH Server 8.41 (WinOS)
Before You Begin
Preparing the SSH Client
Validating the SSH Tunnel
Validating SSH Client File Transfer to the app-server
Validating SSH Commands to the app-server
Validating SSH Local Port Forwarding to the app-server
This post uses a Public/Private key pair for authentication. SSH Tunneling requires the following prerequisites.
An SSH client.
SSH private key(s) corresponding to the public key(s) on the SSH hosts.
The following must be in place. Links to the relevant documentation are provided.
Compartment to contain Virtual Cloud Network(s) (VCNs) Here
Compartment Privilege Policies to create and manage resources Here
VCN(s) with non-overlapping IP Address Ranges (CIDR blocks). See Overview of Networking for an overview and links to this and the following network components.
A Public and a Private Subnet in the VCN(s).
If the Bastion and RDG hosts are in different VCNs then peered gateways and routing rules must be in place. See Here for guidance on peering.
Gateways associated with the subnets allowing outbound traffic from the subnets. See Here for guidance on various gateways.
Route Tables associated with the public and private subnets directing traffic appropriately See Here for guidance on route tables.
The public subnet hosting the bastion instance must have the following.
An Internet Gateway for SSH Server responses to the SSH Client.
A Routing Rule in the subnet's Route Tables directing SSH responses to the Internet Gateway. See Here for guidance on route tables.
A compute Instance with access to the app-server Here
An SSH public key corresponding a private key on the SSH client.
An Ingress rules allowing access to port 22. Port 22 is the default for SSH.
The private subnet hosting the app-server must have the following.
A compute Instance with access back to the bastion host.
An SSH public key corresponding to a private key on the SSH client.
An Ingress rule allowing access to port 22.
The following steps have been tested with the two subnets in the same VCN, locally peered VCNs, and VCNs in different regions remotely peered.
Below are sample diagrams:
This post uses an SSH Client configuration file that contains the addresses of the bastion host and the app-server as well as the paths to the private key for each. The user on the hosts is assumed to be opc. The file is named config and is located in the .ssh folder within a user's home directory e.g. /Users/dcarley/.ssh It is assumed there are no entries existing in the configuration file for hosts named "bastion" and "app-server".
User an editor to insert or append lines to the configuration file for the IP address, username and path to the private key. Example lines are below:
User an editor to insert or append lines to the configuration file for the IP address, username, path to the private key, a proxy parameter that uses the bastion host and a local Port Forward of port 8080. Example lines are below:
Display the contents of the configuration file and ensure the entries are correct. An example command is below:
Note: the '~' notation means your home directory.
No preparation is necessary if using standard Oracle Linux images.
Run the SSH command to connect to the app-server with the opc user via the bastion host. An example command is below:
Answer yes for both hosts to continue and the fingerprints are added to the known_hosts file.
The complete output is shown below.
Edit or create a file in your home directory to be transferred to the app-server via the bastion host.
The following example uses a file named testfile and has the contents "Hello World".
echo "Hello World" > ~/testfile
Use scp to copy the file to the opc home directory on the app-server. scp is a program for copying files between computers using the SSH protocol. An example command is below:
scp ~/testfile app-server:/home/opc
Note: the file is not stored on the bastion host before being transferred to the app-server.
Connect to the app-server and display the file.
Use the same ssh app-server again to connect to the app-server.
Use the cat testfile command to display the contents:
Type exit to return to you client session.
Connect to the bastion host to confirm the file is not stored there.
Use the ssh bastion to connect to the bastion host and issue the cat testfile command again:
Type exit to return to you client session.
You may want to issue a command or commands from your client that runs a program or programs on the app-server. The following creates a local script file, copies it to the server and uses the ssh command on the client to run it on the app-server.
echo "echo Hello World" > localScriptfile.sh; chmod +x localScriptfile.sh;
scp localScriptfile.sh app-server:/home/opc/serverScriptfile.sh
ssh app-server ./serverScriptfile.sh
To avoid opening a port on a server, SSH can use a Local Port Forward to provide client access to the server port via the SSH port e.g. 22. See here for details. The app-server configuration above shows the Local Port Forward parameter.The following allows a browser on the client to access port 8080 on the app-server via port 22.
Note: To avoid a 504 Gateway Timeout Error, ensure the Local port is exactly the same as the RDG port.
This opens the Local Port Forward
Open a bowser window on the client with the address:
This post described configuring an SSH Client to reach an RDG host (app-server) in a private subnet via a bastion host in a public subnet.
For other posts relating to analytics and data integration visit http://www.ateam-oracle.com/dayne-carley