caddy v2 config : https://binbash.fr/topic/306/une-page-de-maintenance-pour-ingress-k8s-avec-caddy-v2

caddy.json

{
    "admin": {
        "listen": ":2019"
    },
    "apps": {
        "http": {
            "servers": {
                "maintenance": {
                    "listen": [
                        ":80"
                    ],
                    "routes": [
                        {
                            "match": [
                                {
                                    "path": [
                                        "/reason"
                                    ]
                                }
                            ],
                            "handle": [
                                {
                                    "handler": "static_response",
                                    "body": ""
                                }
                            ],
                            "terminal": true
                        },
                        {
                            "match": [
                                {
                                    "path_regexp": {
                                        "name": "maintenance",
                                        "pattern": "^(/(?:css|js|img).*)"
                                    }
                                }
                            ],
                            "handle": [
                                {
                                    "handler": "rewrite",
                                    "uri": "/maintenance{http.regexp.maintenance.1}"
                                }
                            ]
                        },
                        {
                            "match": [
                                {
                                    "path_regexp": {
                                        "name": "index",
                                        "pattern": "^/(?:|index\\.html)$"
                                    }
                                }
                            ],
                            "handle": [
                                {
                                    "handler": "rewrite",
                                    "uri": "/maintenance/index.html"
                                }
                            ]
                        },
                        {
                            "match": [
                                {
                                    "not": [{
                                        "path": [
                                            "/maintenance/css*",
                                            "/maintenance/js*",
                                            "/maintenance/img*",
                                            "/maintenance/",
                                            "/maintenance/index.html"
                                        ]
                                    }]
                                }
                            ],
                            "handle": [
                                {
                                    "handler": "rewrite",
                                    "uri": "/maintenance/index.html"
                                }
                            ]
                        },
                        {
                            "handle": [
                                {
                                    "handler": "reverse_proxy",
                                    "transport": {
                                        "protocol": "http",
                                        "tls": {
                                            "insecure_skip_verify": true,
                                            "server_name": "minio"
                                        }
                                    },
                                    "upstreams": [
                                        {
                                            "dial": "1.2.3.4:443"
                                        }
                                    ],
                                    "headers": {
                                        "request": {
                                            "add": {
                                                "host": [
                                                    "minio"
                                                ]
                                            }
                                        }
                                    }
                                }
                            ]
                        }
                    ]
                }
            }
        }
    }
}