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TROUBLESHOOTING.md

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Troubleshooting

Getting Docker working with firewalld (Fedora/CentOS/RHEL)

firewall-cmd --zone=public --add-masquerade --permanent
firewall-cmd --zone=trusted --change-interface=docker 0 --permanent
firewall-cmd --reload

Receiving Docker network errors

Symptom: Starting of challenge instances fails with the message "ERROR: could not create challenge network (cmgr-...): Error response from daemon: could not find an available, non-overlapping IPv4 address pool among the defaults to assign to the network.

Cause: Docker has exhausted all available subnets that it has been assigned and cannot create anymore. By default, Docker only reserves 31 distinct subnets which constrains cmgr to no more than that number of running challenge instances (each instance gets a network).

Solution: Choose a sufficiently large region of RFC 1918 address space and update the Docker daemon's configuration (/etc/docker/daemon.json) to allot more default networks. It is important to ensure that these addresses are not in use by another network segment and that the individual subnets are large enough to handle any multi-host challenges (to include a solver host and the default gateway).

An example configuration which carves the address space into ~2 million subnets is:

{
  "default-address-pools":
    [
      {"base":"10.0.0.0/8", "size":29}
    ]
}

Note: You will need to restart the daemon after changing its configuration.