Configuring IPSec gateways to connect external nodes to a cluster

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Updated at August 6, 2025

Getting started
Configuring security groups
Configuring routing
Setting up IPSec gateways
Troubleshooting
- Errors when using the docker-ce and containerd packages on an external node

With Yandex Managed Service for Kubernetes, you can connect servers from outside Yandex Cloud as Kubernetes cluster nodes. To connect one, first, set up network connectivity between the remote network hosting the external server and the cloud network hosting your Managed Service for Kubernetes cluster. You can do this using a VPN.

Below is an example of establishing network connectivity over the IPSec protocol. Here, the external server is a VM residing in another Yandex Cloud cloud network.

Getting started

Create your main cloud network with three subnets in different availability zones.
In the main network, create a Managed Service for Kubernetes cluster with a highly available master.

To create an external node group, the Managed Service for Kubernetes cluster must operate in tunnel mode. This mode can be enabled only when creating the cluster.
Install kubect and configure it to work with the new cluster.
In the main network, create a Compute Cloud VM with a public IP address; name it VM-1. On this VM, you will set up the main IPSec gateway.
Create an additional cloud network with one subnet.
In the additional network, create a Compute Cloud VM with a public IP address; name it VM-2. You will use this VM to set up the additional IPSec gateway.

Configuring security groups

In the main network, create a security group and assign it to VM-1. Add the following rules to the group:

Outgoing traffic

Incoming traffic

Description	Port range	Protocol	Destination name	CIDR blocks
`any`	`0-65535`	`Any`	`CIDR`	`0.0.0.0/0`

Description	Port range	Protocol	Source	CIDR blocks
`icmp`	`0-65535`	`ICMP`	`CIDR`	`0.0.0.0/0`
`ssh`	`22`	`TCP`	`CIDR`	`0.0.0.0/0`
`ipsec-udp-500`	`500`	`UDP`	`CIDR`	`<VM_2_public_address>/32`
`ipsec-udp-4500`	`4500`	`UDP`	`CIDR`	`<VM_2_public_address>/32`
`VM-2-subnet`	`0-65535`	`Any`	`CIDR`	`<VM_2_subnet_CIDR>`

In the additional network, create a security group and assign it to VM-2. Add the following rules to the group:

Outgoing traffic

Incoming traffic

Description	Port range	Protocol	Destination name	CIDR blocks
`any`	`0-65535`	`Any`	`CIDR`	`0.0.0.0/0`

Description	Port range	Protocol	Source	CIDR blocks
`icmp`	`0-65535`	`ICMP`	`CIDR`	`0.0.0.0/0`
`ssh`	`22`	`TCP`	`CIDR`	`0.0.0.0/0`
`ipsec-udp-500`	`500`	`UDP`	`CIDR`	`<VM_1_public_address>/32`
`ipsec-udp-4500`	`4500`	`UDP`	`CIDR`	`<VM_1_public_address>/32`
`k8s-VM-1-subnets`	`0-65535`	`Any`	`CIDR`	`<main_subnet1_CIDR>`, `<main_subnet2_CIDR>`, `<<main_subnet3_CIDR>`
`cluster&services`	`0-65535`	`Any`	`CIDR`	`<cluster_CIDR>`, `<CIDRs_of_services>`

Add the following rule to the security group of the Managed Service for Kubernetes cluster and node groups:

Incoming traffic

Description Port range Protocol Source CIDR blocks

VM-2-subnet 0-65535 Any CIDR <VM_2_subnet_CIDR>

Description	Port range	Protocol	Source	CIDR blocks
`VM-2-subnet`	`0-65535`	`Any`	`CIDR`	`<VM_2_subnet_CIDR>`

Configuring routing

Configure routing for the main IPSec gateway:
1. In the main network, create a route table and add a static route to it:
  - Destination prefix: Specify the CIDR of the VM-2's subnet.
  - IP address: Specify the VM-1's internal IP address.
2. Associate the route table with all subnets in your main network.
Configure routing for the additional IPSec gateway:
1. In the additional network, create a route table.
2. Add a static route for the route table:
  - Destination prefix: Specify the CIDR of the VM-1's subnet.
  - IP address: Specify the VM-2's internal IP address.
  Repeat this step for each subnet in your main network.
3. Associate the route table to the VM-2's subnet.

Setting up IPSec gateways

Set up the main IPsec gateway:

Connect to VM-1 over SSH.

Install strongSwan:

sudo apt update && sudo apt install strongswan

Open the ipsec.conf configuration file:
```
sudo nano /etc/ipsec.conf
```

Replace the file contents with this text:

# basic configuration

config setup
  charondebug="all"
  uniqueids=yes

conn VM-1
  type=tunnel
  auto=route
  keyexchange=ikev2
  ike=aes256-sha2_256-modp2048!
  esp=aes256-sha2_256!
  authby=secret
  left=<VM_1_internal_address>
  leftsubnet=<main_subnet1_CIDR>,<main_subnet2_CIDR>,<main_subnet3_CIDR>
  leftsourceip=<VM_1_internal_address>
  leftid=<VM_1_public_address>
  right=<VM_2_public_address>
  rightsubnet=<VM_2_subnet_CIDR>
  aggressive=no
  keyingtries=%forever
  ikelifetime=86400s

For more information about parameters, see the strongSwan documentation.

Open the ipsec.secrets file that is used for authentication:
```
sudo nano /etc/ipsec.secrets
```
Replace the file contents with this text:
```
<VM_1_public_address> <VM_2_public_address> : PSK "<password>"
```
To learn more about the ipsec.secrets file format, see the strongSwan documentation.

Set up the additional IPSec gateway:

Connect to VM-2 over SSH.

Install strongSwan:

sudo apt update && sudo apt install strongswan

Open the ipsec.conf configuration file:
```
sudo nano /etc/ipsec.conf
```

Replace the file contents with this text:

# basic configuration

config setup
  charondebug="all"

conn VM-2
  type=tunnel
  auto=route
  keyexchange=ikev2
  ike=aes256-sha2_256-modp2048!
  esp=aes256-sha2_256!
  authby=secret
  left=<VM_2_internal_address>
  leftid=<VM_2_public_address>
  leftsubnet=<VM_2_subnet_CIDR>
  right=<VM_1_public_address>
  rightsubnet=<main_subnet1_CIDR>,<main_subnet2_CIDR>,<main_subnet3_CIDR>
  rightsourceip=<VM_1_internal_address>
  aggressive=no
  keyingtries=%forever
  ikelifetime=86400s
  lifetime=43200s
  lifebytes=576000000
  dpddelay=30s

For more information about parameters, see the strongSwan documentation.

Open the ipsec.secrets file required for authentication:
```
sudo nano /etc/ipsec.secrets
```
Replace the file contents with this text:
```
<VM_2_public_address> <VM_1_public_address> : PSK "<password>"
```
Passwords must be the same for both VMs.

To learn more about the ipsec.secrets file format, see the strongSwan documentation.

Restart strongSwan on both VMs:
```
sudo ipsec restart
```
Check the connection status on both VMs:
```
sudo ipsec statusall
```
You should see ESTABLISHED in the command output, indicating a successfully established connection:
```
...
Security Associations (1 up, 0 connecting):
     VM-1[1]: ESTABLISHED 5 seconds ago, 10.128.*.**[46.21.***.***]...84.201.***.***[84.201.***.***]
...
```
If the connection was not established, try establishing it manually. On the VM-1 VM, run the following command:
```
sudo ipsec up VM-1
```
You may run this command on just one of the VMs.

Configure MTU on both VMs:

ETH_NIC=eth0
sudo iptables -t mangle -A FORWARD -i ${ETH_NIC} -p tcp -m tcp --tcp-flags SYN,RST SYN -m tcpmss --mss 1361:1536 -j TCPMSS --set-mss 1360
sudo iptables -t mangle -A FORWARD -o ${ETH_NIC} -p tcp -m tcp --tcp-flags SYN,RST SYN -m tcpmss --mss 1361:1536 -j TCPMSS --set-mss 1360
echo "net.ipv4.ip_no_pmtu_disc = 1" | sudo tee -a /etc/sysctl.conf
sudo sysctl -p /etc/sysctl.conf

Warning

If you keep the default MTU value, network traffic losses may possibly occur.

Connect VM-2 to the Managed Service for Kubernetes cluster as its external node.

Troubleshooting

Errors when using the `docker-ce` and `containerd` packages on an external node

To diagnose and fix this error:

View the list of services that are not functioning properly:

sudo systemctl --failed

Result:

UNIT LOAD ACTIVE SUB DESCRIPTION
docker.socket loaded failed failed Docker Socket for the API
LOAD = Reflects whether the unit definition was properly loaded.
ACTIVE = The high-level unit activation state, i.e. generalization of SUB.
SUB = The low-level unit activation state, values depend on unit type.
1 loaded units listed.

Check the docker.socket status:

sudo systemctl status docker.socket

Result:

docker.socket - Docker Socket for the API
Loaded: loaded (/lib/systemd/system/docker.socket; disabled; vendor preset: enabled)
Active: failed (Result: exit-code) since Tue 2024-02-10 09:53:37 UTC; 6s ago
Triggers: ● docker.service
Listen: /run/docker.sock (Stream)
CPU: 1ms
Feb 10 09:53:37 ext-node systemd[1]: Starting Docker Socket for the API...
Feb 10 09:53:37 ext-node systemd[7052]: docker.socket: Failed to resolve group docker: No such process
Feb 10 09:53:37 ext-node systemd[1]: docker.socket: Control process exited, code=exited, status=216/GROUP
Feb 10 09:53:37 ext-node systemd[1]: docker.socket: Failed with result 'exit-code'.
Feb 10 09:53:37 ext-node systemd[1]: Failed to listen on Docker Socket for the API.

Look up errors in system logs:

sudo journalctl -xe

Result:

...
Feb 10 09:56:40 ext-node maintainer[19298]: E: Sub-process /usr/bin/dpkg returned an error code (1)
...

Reinstall the packages and fix the errors:
```
sudo apt install -f
```
When the installer prompts you for action with the config.toml file, enter N to keep the current version of the file.

Configuring IPSec gateways to connect external nodes to a cluster

Getting startedGetting started

Configuring security groupsConfiguring security groups

Configuring routingConfiguring routing

Setting up IPSec gatewaysSetting up IPSec gateways

TroubleshootingTroubleshooting

Errors when using the and packages on an external nodeErrors when using the docker-ce and containerd packages on an external node

Was the article helpful?

Getting started

Configuring security groups

Configuring routing

Setting up IPSec gateways

Troubleshooting

Errors when using the `docker-ce` and `containerd` packages on an external node