Onionbalance v3 Installation Guide

This is a step-by-step recipe to help you configure Onionbalance for v3 onions.

This is really one of my favorite recipes: While onions can make many meals instantly delicious, if the right balance is not found there is danger that their strong sulfuric taste can sometimes overpower the rest of the ingredients. It’s vital to maintain the proper onionbalance to really display the apple-like, deliciously savory notes of this vegetable.

Onionbalance implements round-robin like load balancing on top of Tor onion services. A typical Onionbalance deployment will incorporate one frontend servers and multiple backend instances.


Let’s first start with an overview of the Onionbalance design so that you better understand what we are gonna do in this guide. Through the rest of this guide we will assume you understand how both onionbalance and the onion service protocol works. If you already know how onionbalance works, feel free to skip to the next section.


In this picture you see a setup where Onionbalance is used to load-balance over three backend instances. The frontend service is on the right side whereas the three backend instances are in the middle. On the left side there is a Tor client called Alice who visits the load-balanced service using the frontend address dpkhemrbs3oiv2...onion (which is actually 56 characters long but here we cut it for brevity).

Here is how this works in steps (consult the picture to see where the steps actually happen):

[1]: First the three backend instances (which are regular onion services) publish

their descriptors to the Tor directory hashring.

[2]: Then Onionbalance fetches the descriptors of the backend instances from the hashring.

[3]: Onionbalance now extracts the introduction points out of the backend

descriptors, and creates a new superdescriptor that includes a combination of all those introduction points. Then Onionbalance uploads the superdescriptor to the hashring.

[4]: Now the client, Alice, fetches the superdescriptor from the hashring

by visiting dpkhemrbs3oiv2...onion.

[5]: Alice picks an introduction point from the superdescriptor and

introduces herself to it. Because the introduction points actually belong to the backend instances, Alice is actually talking to backend instance #2, effectively getting load-balanced.

The rest of the onion service protocol carries on as normal between the Alice and the backend instance.


This section will give a short overview of what we are going to do in this guide.

  • We will start by setting up the frontend host. We will install Tor and onionbalance to it, and then we will run onionbalance so that it generates a frontend onion service configuration.

  • We will then setup the backend instances by configuring Tor as an onion service and putting it into “onionbalance instance” mode.

  • In the end of the guide, we will setup onionbalance by informing it about the backend instances, and we will start it up. After this, we should have a working onionbalance configuration.

Not too hard right? Let’s start!


To follow this recipe to completion we will need the following ingredients:

  • a host that will run Onionbalance and act as the load balancing frontend

  • two or more hosts that will run the backend Tor instances

We will assume you are using a Linux system and that you are familiar with building C and Python projects and installing their dependencies. We will also assume that you are well familiar with configuring and running Tor onion services.

Time needed

30 minutes


Step 1: Configuring the frontend server (setting up Tor)

Let’s start by logging into our frontend server and installing Tor. You will want a very recent version of Tor (version or newer is sufficient, as long as it includes #31684). If you want to use the latest official Tor master, you can do the following:

$ git clone https://git.torproject.org/tor.git
$ cd tor
$ ./autogen.sh && ./configure && make

by the end of this process you should have a Tor binary at ./src/app/tor. If this is not the case, you might be missing various C dependencies like libssl-dev, libevent-dev, etc.

Now setup a minimal torrc with a control port enabled. As an example:

SocksPort 0
DataDirectory /home/user/frontend_data/

Now start up Tor and let it do its thing.

Feel free to tweak your torrc as you feel (also enable logging), but for the purposes of this guide I assume that your control port is at

Step 2: Configuring the frontend server (setting up onionbalance)

Now, still on the frontend host we need to setup Onionbalance. If you wish to use the Debian package of onionbalance, you will need version 0.2.0-1 or newer to get v3 support, otherwise you can obtain it via git:

$ git clone https://gitlab.torproject.org/tpo/core/onionbalance.git
$ cd onionbalance
$ sudo python3 setup.py install
# Let's create an onionbalance config file.
# -n indicates how many empty backend address slots will be created.
# These can be easily modified with a text editor at any time.
$ onionbalance-config --hs-version v3 -n 2

After the final command you should have a ./config/config.yaml file with a basic onionbalance configuration. The onion address of your frontend service can be found in the bottom of your config file. So if it says

key: dpkhemrbs3oiv2fww5sxs6r2uybczwijzfn2ezy2osaj7iox7kl7nhad.key

the frontend’s onion address is: dpkhemrbs3oiv2fww5sxs6r2uybczwijzfn2ezy2osaj7iox7kl7nhad.onion .

For now, note down the frontend’s onion address and let’s move on to the next step!


If you need to migrate an already existing Tor onion service to Onionbalance, you can use the key directive of the Onionbalance YAML config file to point to the onion service’s private key (hs_ed25519_secret_key). You can then use your existing onion service’s address as your frontend’s address.

So for example if you place your private key in ./config/hs_keys/hs_ed25519_secret_key, your YAML config file might contain a key directive that looks like this:

key: hs_keys/hs_ed25519_secret_key

Step 3: Configuring the backend instances

OK now with the frontend onion address noted down, let’s move to setting up your backend instances:

Login to one of your backend instances and let’s setup Tor. Similar to the step above, you will need to use the latest Tor master for Onionbalance to work (because of #32709).

As before:

$ git clone https://gitweb.torproject.org/tor.git
$ cd tor
$ ./autogen.sh && ./configure && make

Now you will need a torrc file for your backend instance. Your torrc file needs to setup an onion service (and in this case a v3 one) and I’m gonna assume you know how to do that. So far so good but here comes the twist:

  1. Inside the HiddenService block of your torrc file, you need to add the following line: HiddenServiceOnionbalanceInstance 1. Note that if you do not have an existing v3 onion service and you are trying to create one from scratch, you must first start Tor once without this torrc line, otherwise it will fail to start. After the onion service was created, add this line to your torrc file.

  2. In your hidden service directory where the hostname and hs_ed25519_public_key files are living (assuming you moved them previously or started Tor as described at previous step to generate them) you need to create a new file with the name ‘ob_config’ that has the following line inside:

    MasterOnionAddress dpkhemrbs3oiv2fww5sxs6r2uybczwijzfn2ezy2osaj7iox7kl7nhad.onion

    but substitute the onion address above with your frontend’s onion address.

  3. Start (or restart if currently running) the Tor process to apply the changes.

The points (1) and (2) above are extremely important and if you didn’t do them correctly, nothing is gonna work. If you want to ensure that you did things correctly, start up Tor, and check that your notice log file includes the following line:

[notice] ob_option_parse(): Onionbalance: MasterOnionAddress dpkhemrbs3oiv2fww5sxs6r2uybczwijzfn2ezy2osaj7iox7kl7nhad.onion registered

If you don’t see that, then something went wrong. Please try again from the beginning of this section till you make it! This is the hardest part of the guide too, so if you can do that you can do anything (fwiw, we are at 75% of the whole procedure right now).

After you get that, also make sure that your instances are directly reachable (e.g. using Tor browser). If they are not reachable, then onionbalance won’t be able to see them either and things are not gonna work.

OK, you are done with this backend instance! Now do the same for the other backend instances and note down the onion addresses of your backend instances because we are gonna need them for the next and final step.

Step 4: Start onionbalance!

OK now let’s login back to the frontend server! Go to your onionbalance config file and add your instance addresses in the right fields. In the end it should look like this (for a setup with 3 backend instances):

- instances:
  - address: wmilwokvqistssclrjdi5arzrctn6bznkwmosvfyobmyv2fc3idbpwyd.onion
    name: node1
  - address: fp32xzad7wlnpd4n7jltrb3w3xyj23ppgsnuzhhkzlhbt5337aw2joad.onion
    name: node2
  - address: u6uoeftsysttxeheyxtgdxssnhutmoo2y2rw6igh5ez4hpxaz4dap7ad.onion
    name: node3
  key: dpkhemrbs3oiv2fww5sxs6r2uybczwijzfn2ezy2osaj7iox7kl7nhad.key

Backend instances can be added, removed or edited at any time simply by following the above format. Onionbalance must be restarted after any change of the config file.

Now let’s fire up onionbalance by running the following command (assuming your ControlPort torrc setting is 6666, substitute if different):

$ onionbalance -v info -c config/config.yaml -p 6666

If everything went right, onionbalance should start running and after about 10 minutes your frontend service should be reachable via the dpkhemrbs3oiv2fww5sxs6r2uybczwijzfn2ezy2osaj7iox7kl7nhad.onion address!

If something did not go right, that’s OK too, don’t get sad because this was quite complicated. Please check all your logs and make sure you did everything right according to this guide. Keep on hammering at it and you are gonna get it. If nothing seems to work, please get in touch with some details and I can try to help you.

Now What?

Now that you managed to make it work, please monitor your frontend service and make sure that it’s reachable all the time. Check your logs for any errors or bugs and let me know if you see any. If you want you can make onionbalance logging calmer by using the -v warning switch.

You can also setup a Status Socket to monitor Onionbalance.

If you find bugs or do any quick bugfixes, please submit them over Gitlab or Github!


Here are a few common issues you might encounter during your setup.

Permission issues

In order for this to work, the user you are trying to run onionbalance from should have permissions to reach Tor’s control port cookie. Othwerise, you will see an error like this:

[ERROR]: Unable to authenticate on the Tor control connection: Authentication failed: unable to read '/run/tor/control.authcookie' ([Errno 13] Permission denied: '/run/tor/control.authcookie')

As always, we do not recommend running anything as root, when you don’t really have to. In Debian, Tor is run by its dedicated user debian-tor, but it’s not the same for other Linux distributions, so you need to check. In Debian you can add the user you are running onionbalance from to the same sudoers group in order to gain permission:

$ sudo adduser $USER debian-tor