# Polling Tentacles with HA

Listening Tentacles require no special configuration for Octopus High Availability. Polling Tentacles and Kubernetes agents, however, poll a server at regular intervals to check if there are any tasks waiting for the Tentacle to perform. In a High Availability scenario Polling Tentacles must poll all Octopus Server nodes in your configuration. To configure the Kubernetes agent with Octopus High Availability, see [Kubernetes agent HA Cluster Support](/docs/infrastructure/deployment-targets/kubernetes/kubernetes-agent/ha-cluster-support).

## Connecting Polling Tentacles

While a Tentacle could poll a load balancer in an Octopus High Availability cluster, there is a risk, depending on your load balancer configuration, that the Tentacle will not poll all servers in a timely manner.

We recommend two options when configuring Polling Tentacles to connect to your Octopus High Availability cluster:

- Using a **unique address**, and the same listening port (`10943` by default) for each node.
- Using the same address and a **unique port** for each node.

These are discussed further in the next sections.

### Using a unique address

In this scenario, no load balancer is required. Instead, each Octopus node would be configured to listen on the same port (`10943` by default) for inbound traffic. In addition, each node would be able to be reached directly by your Polling Tentacle on a unique address for the node.

For each node in your HA cluster:

- Ensure the communication port Octopus listens on (`10943` by default) is open, including any firewall.
- Register the node with the [Poll Server command line](/docs/octopus-rest-api/tentacle.exe-command-line/poll-server) option. Specify the unique address for the node, including the listening port. For example, in a three-node cluster:
    - Node1 would use address: **Octo1.domain.com:10943**
    - Node2 would use address: **Octo2.domain.com:10943**
    - Node3 would use address: **Octo3.domain.com:10943**

The important thing to remember is that each node should be using a **unique address** and the **same port**.

:::div{.hint}
**Tip:**
A Polling Tentacle will connect to the Octopus Rest API over ports 80 or 443 when it is registering itself with the Octopus Server. After that, it will connect over port `10943` (by default) with the Octopus Server node.

It's important to ensure that any firewalls also allow port 80 or 443 for the initial Tentacle registration.
:::

### Using a unique port

In this scenario, a type of [Network Address Translation (NAT)](https://en.wikipedia.org/wiki/Network_address_translation) is leveraged by using the same address and **unique ports**, usually routed through a load balancer or other network device. Each Octopus node would be configured to listen on a different port (starting at `10943` by default) for inbound traffic.

:::div{.hint}
The advantage of using unique ports is that the Polling Tentacle doesn't need to know each node's address, only the port. The address translation is handled by the load balancer. This allows each node to have a private IP address, with no public access from outside your network required.
:::

Imagine a three-node HA cluster. For each one, we expose a different port to listen on using the [Octopus.Server configure command](/docs/octopus-rest-api/octopus.server.exe-command-line/configure):

- Node1 - Port `10943`
- Node2 - Port `10944`
- Node3 - Port `10945`

Next on the load balancer, create Network Address Translation (NAT) rules and point them to each node in your HA Cluster:

- Open port `10943` and route traffic to **Node1** in your HA Cluster
- Open port `10944` and route traffic to **Node2** in your HA Cluster
- Open port `10945` and route traffic to **Node3** in your HA Cluster
- Continue for any additional nodes in your HA cluster.

If you configured your nodes to use a different listening port, replace `10943`-`10945` with your port range.

The important thing to remember is that each node should be using the **same address** and a **different port**.

## Registering Polling Tentacles

There are two options to add Octopus Servers to a Polling Tentacle: the command line, or editing the Tentacle.config file directly.

Both methods need the Tentacle service restarted afterwards. A running Tentacle doesn't pick up a new server address until it restarts.

**Command line:**

The command line is the preferred option. Run the command once per server; an example command using the default instance can be seen below:

```text
C:\Program Files\Octopus Deploy\Tentacle>Tentacle poll-server --server=https://your-octopus-url --apikey=API-YOUR-KEY
```

Once you've added every node in your cluster, restart the Tentacle service:

```text
C:\Program Files\Octopus Deploy\Tentacle>Tentacle service --restart
```

For more information on these commands, see the [Tentacle poll-server](/docs/octopus-rest-api/tentacle.exe-command-line/poll-server) and [Tentacle service](/docs/octopus-rest-api/tentacle.exe-command-line/service) command line options.

**Tentacle.config:**

Alternatively you can edit Tentacle.config directly to add each Octopus Server (this is interpreted as a JSON array of servers). This method isn't recommended, as editing the JSON array by hand is error-prone. Restart the Tentacle service after you've saved your changes.

```xml
<set key="Tentacle.Communication.TrustedOctopusServers">
[
  {"Thumbprint":"77751F90F9EEDCEE0C0CD84F7A3CC726AD123FA6","CommunicationStyle":2,"Address":"https://10.0.255.160:10943","Squid":null,"SubscriptionId":"poll://g3662re9njtelsyfhm7t/"},
  {"Thumbprint":"77751F90F9EEDCEE0C0CD84F7A3CC726AD123FA6","CommunicationStyle":2,"Address":"https://10.0.255.161:10943","Squid":null,"SubscriptionId":"poll://g3662re9njtelsyfhm7t/"},
  {"Thumbprint":"77751F90F9EEDCEE0C0CD84F7A3CC726AD123FA6","CommunicationStyle":2,"Address":"https://10.0.255.162:10943","Squid":null,"SubscriptionId":"poll://g3662re9njtelsyfhm7t/"}
]
</set>
```

:::div{.hint}
Notice there is an address entry for **each** Octopus Server in the High Availability configuration.
:::