Circus is built on the top of the ZeroMQ library and comes with no security at all in its protocols. However, you can run a Circus system on a server and set up an SSH tunnel to access it from another machine.

This section explains what Circus does on your system when you run it, and ends up describing how to use an SSH tunnel.

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TCP ports

By default, Circus opens the following TCP ports on the local host:

  • 5555 – the port used to control circus via circusctl
  • 5556 – the port used for the Publisher/Subscriber channel.
  • 5557 – the port used for the statistics channel – if activated.
  • 8080 – the port used by the Web UI – if activated.

These ports allow client apps to interact with your Circus system, and depending on how your infrastructure is organized, you may want to protect these ports via firewalls or configure Circus to run using IPC ports.

Here’s an example of running Circus using only IPC entry points:

check_delay = 5
endpoint = ipc:///var/circus/endpoint
pubsub_endpoint = ipc:///var/circus/pubsub
stats_endpoint = ipc:///var/circus/stats

When Configured using IPC, the commands must be run from the same box, but no one can access them from outside, unlike using TCP. The commands must also be run as a user that has write access to the ipc socket paths. You can modify the owner of the endpoint using the endpoint_owner config option. This allows you to run circusd as the root user, but allow non-root processes to send commands to circusd. Note that when using endpoint_owner, in order to prevent non-root processes from being able to start arbitrary processes that run with greater privileges, the add command will enforce that new Watchers must run as the endpoint_owner user. Watcher definitions in the local config files will not be restricted this way.

Of course, if you activate the Web UI, the 8080 port will still be open.


When you run circushttpd manually, or when you use the httpd option in the ini file like this:

check_delay = 5
endpoint = ipc:///var/circus/endpoint
pubsub_endpoint = ipc:///var/circus/pubsub
stats_endpoint = ipc:///var/circus/stats
httpd = 1

The web application will run on port 8080 and will let anyone accessing the web page manage the circusd daemon.

That includes creating new watchers that can run any command on your system !

Do not make it publicly available

If you want to protect the access to the web panel, you can serve it behind Nginx or Apache or any proxy-capable web server, that can take care of the security.

User and Group Permissions

By default, all processes started with Circus will be running with the same user and group as circusd. Depending on the privileges the user has on the system, you may not have access to all the features Circus provides.

For instance, some statistics features on a running processes require extended privileges. Typically, if the CPU usage numbers you get using the stats command are N/A, it means your user can’t access the proc files. This will be the case by default under Mac OS X.

You may run circusd as root to fix this, and set the uid and gid values for each watcher to get all the features.

But beware that running circusd as root exposes you to potential privilege escalation bugs. While we’re doing our best to avoid any bugs, running as root and facing a bug that performs unwanted actions on your system may be dangerous.

The best way to prevent this is to make sure that the system running Circus is completely isolated (like a VM) or to run the whole system under a controlled user.

SSH tunneling

Clients can connect to a circusd instance by creating an SSH tunnel. To do so, pass the command line option –ssh followed by user@address, where user is the user on the remote server and address is the server’s address as seen by the client. The SSH protocol will require credentials to complete the login.

If circusd as seen by the SSH server is not at the default endpoint address localhost:5555 then specify the circusd address using the option –endpoint

Secured setup example

Setting up a secured Circus server can be done by:

  • Running an SSH Server
  • Running Apache or Nginx on the 80 port, and doing a reverse-proxy on the 8080 port.
  • Blocking the 8080 port from outside access.
  • Running all ZMQ Circusd ports using IPC files instead of TCP ports, and tunneling all calls via SSH.