可以添加一些回退逻辑来处理负载均衡器的存在。

此外，通过检查，即使没有负载均衡器，X-Forwarded-For报头也会被设置(可能是因为额外的Kestrel层?):

public string GetRequestIP(bool tryUseXForwardHeader = true)
{
    string ip = null;

    // todo support new "Forwarded" header (2014) https://en.wikipedia.org/wiki/X-Forwarded-For

    // X-Forwarded-For (csv list):  Using the First entry in the list seems to work
    // for 99% of cases however it has been suggested that a better (although tedious)
    // approach might be to read each IP from right to left and use the first public IP.
    // http://stackoverflow.com/a/43554000/538763
    //
    if (tryUseXForwardHeader)
        ip = GetHeaderValueAs<string>("X-Forwarded-For").SplitCsv().FirstOrDefault();

    // RemoteIpAddress is always null in DNX RC1 Update1 (bug).
    if (ip.IsNullOrWhitespace() && _httpContextAccessor.HttpContext?.Connection?.RemoteIpAddress != null)
        ip = _httpContextAccessor.HttpContext.Connection.RemoteIpAddress.ToString();

    if (ip.IsNullOrWhitespace())
        ip = GetHeaderValueAs<string>("REMOTE_ADDR");

    // _httpContextAccessor.HttpContext?.Request?.Host this is the local host.

    if (ip.IsNullOrWhitespace())
        throw new Exception("Unable to determine caller's IP.");

    return ip;
}

public T GetHeaderValueAs<T>(string headerName)
{
    StringValues values;

    if (_httpContextAccessor.HttpContext?.Request?.Headers?.TryGetValue(headerName, out values) ?? false)
    {
        string rawValues = values.ToString();   // writes out as Csv when there are multiple.

        if (!rawValues.IsNullOrWhitespace())
            return (T)Convert.ChangeType(values.ToString(), typeof(T));
    }
    return default(T);
}

public static List<string> SplitCsv(this string csvList, bool nullOrWhitespaceInputReturnsNull = false)
{
    if (string.IsNullOrWhiteSpace(csvList))
        return nullOrWhitespaceInputReturnsNull ? null : new List<string>();

    return csvList
        .TrimEnd(',')
        .Split(',')
        .AsEnumerable<string>()
        .Select(s => s.Trim())
        .ToList();
}

public static bool IsNullOrWhitespace(this string s)
{
    return String.IsNullOrWhiteSpace(s);
}

假设_httpContextAccessor通过DI提供。

可以添加一些回退逻辑来处理负载均衡器的存在。

此外，通过检查，即使没有负载均衡器，X-Forwarded-For报头也会被设置(可能是因为额外的Kestrel层?):

public string GetRequestIP(bool tryUseXForwardHeader = true)
{
    string ip = null;

    // todo support new "Forwarded" header (2014) https://en.wikipedia.org/wiki/X-Forwarded-For

    // X-Forwarded-For (csv list):  Using the First entry in the list seems to work
    // for 99% of cases however it has been suggested that a better (although tedious)
    // approach might be to read each IP from right to left and use the first public IP.
    // http://stackoverflow.com/a/43554000/538763
    //
    if (tryUseXForwardHeader)
        ip = GetHeaderValueAs<string>("X-Forwarded-For").SplitCsv().FirstOrDefault();

    // RemoteIpAddress is always null in DNX RC1 Update1 (bug).
    if (ip.IsNullOrWhitespace() && _httpContextAccessor.HttpContext?.Connection?.RemoteIpAddress != null)
        ip = _httpContextAccessor.HttpContext.Connection.RemoteIpAddress.ToString();

    if (ip.IsNullOrWhitespace())
        ip = GetHeaderValueAs<string>("REMOTE_ADDR");

    // _httpContextAccessor.HttpContext?.Request?.Host this is the local host.

    if (ip.IsNullOrWhitespace())
        throw new Exception("Unable to determine caller's IP.");

    return ip;
}

public T GetHeaderValueAs<T>(string headerName)
{
    StringValues values;

    if (_httpContextAccessor.HttpContext?.Request?.Headers?.TryGetValue(headerName, out values) ?? false)
    {
        string rawValues = values.ToString();   // writes out as Csv when there are multiple.

        if (!rawValues.IsNullOrWhitespace())
            return (T)Convert.ChangeType(values.ToString(), typeof(T));
    }
    return default(T);
}

public static List<string> SplitCsv(this string csvList, bool nullOrWhitespaceInputReturnsNull = false)
{
    if (string.IsNullOrWhiteSpace(csvList))
        return nullOrWhitespaceInputReturnsNull ? null : new List<string>();

    return csvList
        .TrimEnd(',')
        .Split(',')
        .AsEnumerable<string>()
        .Select(s => s.Trim())
        .ToList();
}

public static bool IsNullOrWhitespace(this string s)
{
    return String.IsNullOrWhiteSpace(s);
}

假设_httpContextAccessor通过DI提供。

您可以使用IHttpConnectionFeature来获取此信息。

var remoteIpAddress = httpContext.GetFeature<IHttpConnectionFeature>()?.RemoteIpAddress;

也可以从外部服务获取IP。

public string GetIP()
{
    HttpClient client = new HttpClient();
    var result = client.GetStringAsync("https://jsonip.com/").Result;
    var ip = JsonSerializer.Deserialize<RemoteIPDto>(result.ToString()).IP;
    return ip;
}

RemoteIPDto类在哪里

public class RemoteIPDto
{
    [JsonPropertyName("ip")]
    public string IP { get; set; }
    [JsonPropertyName("geo-ip")]
    public string GeoIp { get; set; }
    [JsonPropertyName("API Help")]
    public string ApiHelp { get; set; }
}

在我的情况下，我用docker和nginx作为反向代理在DigitalOcean上运行DotNet Core 2.2 Web应用程序。使用Startup.cs中的这段代码，我可以获得客户端IP

app.UseForwardedHeaders(new ForwardedHeadersOptions
        {
            ForwardedHeaders = ForwardedHeaders.All,
            RequireHeaderSymmetry = false,
            ForwardLimit = null,
            KnownNetworks = { new IPNetwork(IPAddress.Parse("::ffff:172.17.0.1"), 104) }
        });

::ffff:172.17.0.1是我在使用之前获得的ip

Request.HttpContext.Connection.RemoteIpAddress.ToString();

根据官方文档，如果你使用Apache或Nginx集成，以下代码应该添加到启动。ConfigureServices方法。

// using Microsoft.AspNetCore.HttpOverrides;

    services.Configure<ForwardedHeadersOptions>(options =>
    {
        options.ForwardedHeaders = ForwardedHeaders.XForwardedFor | 
            ForwardedHeaders.XForwardedProto;
        // Only loopback proxies are allowed by default.
        // Clear that restriction because forwarders are enabled by explicit 
        // configuration.
        options.KnownNetworks.Clear();
        options.KnownProxies.Clear();
    });

最重要的是，在配置方法中使用

app.UseForwardedHeaders();

进一步假设在nginx conf文件中，在一个位置内，使用

proxy_set_header   Host $host;
proxy_set_header   X-Real-IP $remote_addr;
proxy_set_header   X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header   X-Forwarded-Host $server_name;

现在X-Forwarded-For中的第一个条目将是真正的客户端IP。

重要:如果你想保护应用程序，不允许攻击者注入x - forward - for，请阅读这个答案。

请参见转发Linux和非iis反向代理方案、配置Nginx和处理无效报头