liquibase-core/src/main/java/liquibase/integration/servlet/LiquibaseServletListener.java
private boolean checkPreconditions(ServletContext servletContext, InitialContext ic) {
        GlobalConfiguration globalConfiguration = LiquibaseConfiguration.getInstance().getConfiguration(GlobalConfiguration.class);
        if (!globalConfiguration.getShouldRun()) {
            Scope.getCurrentScope().getLog(getClass()).info(LogType.LOG, "Liquibase did not run on " + hostName
                    + " because "+ LiquibaseConfiguration.getInstance().describeValueLookupLogic(globalConfiguration.getProperty(GlobalConfiguration.SHOULD_RUN))
                            + " was set to false");
            return false;
        }

        String machineIncludes = (String) servletValueContainer.getValue(LIQUIBASE_HOST_INCLUDES);
        String machineExcludes = (String) servletValueContainer.getValue(LIQUIBASE_HOST_EXCLUDES);

        boolean shouldRun = false;
        if ((machineIncludes == null) && (machineExcludes == null)) {
            shouldRun = true;
        } else if (machineIncludes != null) {
            for (String machine : machineIncludes.split(",")) {
                machine = machine.trim();
                if (hostName.equalsIgnoreCase(machine)) {
                    shouldRun = true;
                }
            }
        } else if (machineExcludes != null) {
            shouldRun = true;
            for (String machine : machineExcludes.split(",")) {
                machine = machine.trim();
                if (hostName.equalsIgnoreCase(machine)) {
                    shouldRun = false;
                }
            }
        }

        if (globalConfiguration.getShouldRun() && globalConfiguration.getProperty(GlobalConfiguration.SHOULD_RUN).getWasOverridden()) {
            shouldRun = true;
            servletContext.log("ignoring " + LIQUIBASE_HOST_INCLUDES + " and "
                    + LIQUIBASE_HOST_EXCLUDES + ", since " + LiquibaseConfiguration.getInstance().describeValueLookupLogic(globalConfiguration.getProperty(GlobalConfiguration.SHOULD_RUN))
                    + "=true");
        }
        if (!shouldRun) {
            servletContext.log("LiquibaseServletListener did not run due to "
                    + LIQUIBASE_HOST_INCLUDES + " and/or " + LIQUIBASE_HOST_EXCLUDES + "");
            return false;
        }
        return true;
    }
private boolean checkPreconditions(ServletContext servletContext, InitialContext ic) {
        GlobalConfiguration globalConfiguration = LiquibaseConfiguration.getInstance().getConfiguration(GlobalConfiguration.class);
        if (!globalConfiguration.getShouldRun()) {
            Scope.getCurrentScope().getLog(getClass()).info(LogType.LOG, "Liquibase did not run on " + hostName
                    + " because "+ LiquibaseConfiguration.getInstance().describeValueLookupLogic(globalConfiguration.getProperty(GlobalConfiguration.SHOULD_RUN))
                            + " was set to false");
            return false;
        }

        String machineIncludes = (String) servletValueContainer.getValue(LIQUIBASE_HOST_INCLUDES);
        String machineExcludes = (String) servletValueContainer.getValue(LIQUIBASE_HOST_EXCLUDES);

        boolean shouldRun = false;
        if ((machineIncludes == null) && (machineExcludes == null)) {
            shouldRun = true;
        } else if (machineIncludes != null) {
            for (String machine : machineIncludes.split(",")) {
                machine = machine.trim();
                if (hostName.equalsIgnoreCase(machine)) {
                    shouldRun = true;
                }
            }
        } else if (machineExcludes != null) {
            shouldRun = true;
            for (String machine : machineExcludes.split(",")) {
                machine = machine.trim();
                if (hostName.equalsIgnoreCase(machine)) {
                    shouldRun = false;
                }
            }
        }

        if (globalConfiguration.getShouldRun() && globalConfiguration.getProperty(GlobalConfiguration.SHOULD_RUN).getWasOverridden()) {
            shouldRun = true;
            servletContext.log("ignoring " + LIQUIBASE_HOST_INCLUDES + " and "
                    + LIQUIBASE_HOST_EXCLUDES + ", since " + LiquibaseConfiguration.getInstance().describeValueLookupLogic(globalConfiguration.getProperty(GlobalConfiguration.SHOULD_RUN))
                    + "=true");
        }
        if (!shouldRun) {
            servletContext.log("LiquibaseServletListener did not run due to "
                    + LIQUIBASE_HOST_INCLUDES + " and/or " + LIQUIBASE_HOST_EXCLUDES + "");
            return false;
        }
        return true;
    }
Checks if the update is supposed to be executed. That depends on several conditions:
<ol>
<li>if liquibase.shouldRun is <code>false</code> the update will not be executed.</li>
<li>if {@value LiquibaseServletListener#LIQUIBASE_HOST_INCLUDES} contains the current hostname, the the update will be executed.</li>
<li>if {@value LiquibaseServletListener#LIQUIBASE_HOST_EXCLUDES} contains the current hostname, the the update will not be executed.</li>
</ol>