[Fix] Use default gateway, when bridge network doesn't have it (#666, @kuritka)

[kuritka]

What

If there is no default gateway in the bridge network, k3d crashes because it tries to parse the empty gateway string. This PR will use the default gateway if the gateway does not exist. A cluster can be created than.

Why

For some time docker does not create an automatic gateway in case I create a new network. When I create a bridge network without a gateway and try to connect it to k3d, the cluster installation of the latest versions of k3d crashes.

For example, this won't work for me:

docker network create my-network --subnet=172.18.0.0/16
k3d cluster create my-cluster --network=my-network

        "IPAM": {
            "Driver": "default",
            "Options": {},
            "Config": [
                {
                    "Subnet": "172.18.0.0/16"
                }
            ]
        },

Right now we have to do something like this manually:

docker network create my-gw-network --subnet=172.22.0.0/16 --gateway=172.22.0.1
k3d cluster create my-cluster --network=my-gw-network

        "IPAM": {
            "Driver": "default",
            "Options": {},
            "Config": [
                {
                    "Subnet": "172.22.0.0/16",
                    "Gateway": "172.22.0.1"
                }
            ]
        },

^^^ passing

Implications

our k3d action worked fine on k3d v4.4.1, until 28.6.2021, when the GitHub runner upgraded to Ubuntu Version: 20210628.1. This forced us to upgrade k3d-action a bit earlier than we had planned. Unfortunately, we found out that the newer implementation can't handle the missing gateway. This change does not affect the CLI or Docker settings. It only handles internally the case when the gateway is missing in docker network settings.

@all-contributors add @kuritka for code, maintenance

Signed-off-by: kuritka kuritka@gmail.com

[iwilltry42]

Hi @kuritka , thanks for this PR!
Changes in the GH Actions VM may also explain #663.
The addition makes total sense for me, thank you!

[iwilltry42]

LGTM

[huapox]

same with k3d v5.7.x

err with docker network create k3d-network --subnet=10.28.0.0/24

INFO[0000] Deleting cluster 'clust1'                    
INFO[0001] Deleting cluster network 'k3d-clust1'        
INFO[0001] Deleting 1 attached volumes...               
INFO[0001] Removing cluster details from default kubeconfig... 
INFO[0001] Removing standalone kubeconfig file (if there is one)... 
INFO[0001] Successfully deleted cluster clust1!         
INFO[0000] Using config file ./k3d-config.yaml (k3d.io/v1alpha5#simple) 
INFO[0000] Prep: Network                                
INFO[0000] Re-using existing network 'k3d-network' (6dd07994a6f9a0b6dcb1e5c1508a15610b485878488bcaa06616fcafb6443ee5) 
INFO[0000] Created image volume k3d-clust1-images       
INFO[0000] Creating node 'default.registry.local'       
INFO[0000] Successfully created registry 'default.registry.local' 
INFO[0000] Starting new tools node...                   
INFO[0000] Starting node 'k3d-clust1-tools'             
INFO[0001] Creating node 'k3d-clust1-server-0'          
INFO[0001] Creating node 'k3d-clust1-agent-0'           
INFO[0001] Creating node 'k3d-clust1-agent-1'           
INFO[0001] Using the k3d-tools node to gather environment information 
ERRO[0001] failed to gather environment information used for cluster creation: failed to get host IP: runtime failed to get host IP: failed to get gateway IP of docker network 'k3d-network': no gateway defined for n
ERRO[0001] Failed to create cluster >>> Rolling Back    
INFO[0001] Deleting cluster 'clust1'                    
INFO[0001] Deleting 1 attached volumes...               
FATA[0001] Cluster creation FAILED, all changes have been rolled back!

works with docker network create k3d-gw-network --subnet=10.29.0.0/24 --gateway=10.29.0.1

INFO[0000] No nodes found for cluster 'clust1', nothing to delete. 
INFO[0000] No clusters found                            
INFO[0000] Using config file ./k3d-config.yaml (k3d.io/v1alpha5#simple) 
INFO[0000] Prep: Network                                
INFO[0000] Re-using existing network 'k3d-gw-network' (b2806a70703acb7ab1ebdd4abc8c3110c3515841439c3b112ffbdfae4adcf6af) 
INFO[0000] Created image volume k3d-clust1-images       
INFO[0000] Creating node 'default.registry.local'       
INFO[0000] Successfully created registry 'default.registry.local' 
INFO[0000] Starting new tools node...                   
INFO[0000] Starting node 'k3d-clust1-tools'             
INFO[0001] Creating node 'k3d-clust1-server-0'          
INFO[0001] Creating node 'k3d-clust1-agent-0'           
INFO[0001] Creating node 'k3d-clust1-agent-1'           
INFO[0001] Using the k3d-tools node to gather environment information 
INFO[0001] HostIP: using network gateway 10.29.0.1 address 
INFO[0001] Starting cluster 'clust1'                    
INFO[0001] Starting servers...                          
INFO[0001] Starting node 'k3d-clust1-server-0'          
INFO[0005] Starting agents...                           
INFO[0006] Starting node 'k3d-clust1-agent-0'           
INFO[0006] Starting node 'k3d-clust1-agent-1'           
INFO[0009] Starting helpers...                          
INFO[0009] Starting node 'default.registry.local'       
INFO[0009] Injecting records for hostAliases (incl. host.k3d.internal) and for 4 network members into CoreDNS configmap... 
INFO[0012] Cluster 'clust1' created successfully!       
INFO[0013] You can now use it like this: