MyCATApache/Mycat-Server · error · ConfigException

host duplicated

Error message

host duplicated : ${host}

What it means

XMLServerLoader.loadFirewall parses the <firewall><host> section of server.xml, which maps host patterns to allowed users. Each host value must not already be registered in the firewall's host table; if firewall.existsHost(host) is true while adding, it throws this ConfigException. Duplicate host entries would make whitelist enforcement ambiguous.

Solutions

1. Open server.xml's <firewall> section and remove or merge duplicate host entries so each host/IP appears only once across all <host> elements
2. If one host needs multiple users, list several users in the single host element's user attribute instead of duplicating the host
3. Check comma-separated lists within one attribute for repeated values after trimming
4. Restart MyCat after deduplicating

Example fix

// before
<host host="10.0.0.1" user="user1"/>
<host host="10.0.0.1" user="user2"/>
// after
<host host="10.0.0.1" user="user1,user2"/>

// detect duplicate hosts in server.xml firewall section
Set<String> seen = new HashSet<>();
NodeList hs = doc.getElementsByTagName("host");
for (int i = 0; i < hs.getLength(); i++) {
    for (String h : ((Element) hs.item(i)).getAttribute("host").split(",")) {
        if (!seen.add(h.trim())) throw new IllegalStateException("Duplicate firewall host: " + h);
    }
}

null

try {
    serverLoader.load();
} catch (ConfigException e) {
    LOG.error("Firewall host duplication in server.xml: " + e.getMessage());
    throw new ConfigurationException("Each whitelisted host may appear only once", e);
}

When it happens

Trigger: Loading server.xml at startup; a <host host="10.0.0.1"> element lists an IP/host that a previous <host> element (or an earlier entry in the same comma-separated list) already registered.

Common situations: Repeating the same IP in two <host> elements to grant different user groups; including the same host twice within one comma-separated host attribute; merging server.xml fragments that both whitelist the same host.

Understand the failure class

Background: Conflicting config options: "cannot be used together" — configuration validation errors across open-source libraries — this error's family across 162 libraries.

Related errors

• dataHost name duplicated!
• writeHost duplicated!
• readHost duplicated!
• [user: ] doesn't exist in [host: ]
• [host: ] contains one root privileges user

AI-assisted analysis of MyCATApache/Mycat-Server@65f8d8beb7 (2026-09-11). Data as JSON: /api/errors/8a2b51453075467d. Report an issue: GitHub.

Appendix: source

Thrown at src/main/java/io/mycat/config/loader/xml/XMLServerLoader.java:152

     * @date 2016/12/8
     * @modifiedBy Hash Zhang
     */
    private void loadFirewall(Element root) throws IllegalAccessException, InvocationTargetException {
        NodeList list = root.getElementsByTagName("host");
        Map<String, List<UserConfig>> whitehost = new HashMap<>();
        Map<Pattern, List<UserConfig>> whitehostMask = new HashMap<>();

        for (int i = 0, n = list.getLength(); i < n; i++) {
            Node node = list.item(i);
            if (node instanceof Element) {
                Element e = (Element) node;
                String hostStr = e.getAttribute("host").trim();
                String userStr = e.getAttribute("user").trim();
                String []hosts = hostStr.split(",");
                for (String host : hosts) {
                    host = host.trim();
                    if (this.firewall.existsHost(host)) {
                        throw new ConfigException("host duplicated : " + host);
                    }
                }
                String []users = userStr.split(",");
                List<UserConfig> userConfigs = new ArrayList<UserConfig>();
                for(String user : users){
                    user = user.trim();
                	UserConfig uc = this.users.get(user);
                    if (null == uc) {
                        throw new ConfigException("[user: " + user + "] doesn't exist in [host: " + hostStr + "]");
                    }
                    if (uc.getSchemas() == null || uc.getSchemas().size() == 0) {
                        throw new ConfigException("[host: " + hostStr + "] contains one root privileges user: " + user);
                    }
                    userConfigs.add(uc);
                }
                for (String host : hosts) {
                    host = host.trim();
                    if (host.contains("*") || host.contains("%")) {

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