Knowledge Worth Spreading

ECONNRESET when making thousands requests

In situation doing thousands of http requests, it is easy to get error ECONNRESET, for example :

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require('isomorphic-fetch');

const promises = []
for(var i=0; i<10000; i++){
    promises.push(fetch('http://example.com/'+i));
}

const results = await Promise.all(promises)

To find ports status on windows, there is a default Windows GUI - Resource Monitor or you could use netstat via command prompt.

Today When I connect to Windows through Remote Desktop Viewer got error connecting to host prompt.
After searching the solution is to remove the server I’m having issue in $home/.freerdp/known_hosts and reconnecting again.

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[sing@study ~]$ vi ~/.freerdp/known_hosts
# In Vim, remove the line start with server ip you are connecting to by `dd`, and `:wq` to save the file.

Reference: https://superuser.com/questions/834447/vinagre-remote-desktop-viewer-for-gnome-isnt-working-out-of-box

PostAsync

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static readonly HttpClient Client = new HttpClient();
public async Task<T> PostAsync<T>(string url, object data) where T : class, new()
{
    try
    {
        string content = JsonConvert.SerializeObject(data);
        var buffer = Encoding.UTF8.GetBytes(content);
        var byteContent = new ByteArrayContent(buffer);
        byteContent.Headers.ContentType = new MediaTypeHeaderValue("application/json");
        var response = await Client.PostAsync(url, byteContent).ConfigureAwait(false);
        string result = await response.Content.ReadAsStringAsync();
        if (response.StatusCode != HttpStatusCode.OK)
        {
            logger.Error($"GetAsync End, url:{url}, HttpStatusCode:{response.StatusCode}, result:{result}");
            return new T();
        }
        logger.Info($"GetAsync End, url:{url}, result:{result}");
        return JsonConvert.DeserializeObject<T>(result);
    }
    catch (WebException ex)
    {
        if (ex.Response != null)
        {
            string responseContent = new StreamReader(ex.Response.GetResponseStream()).ReadToEnd();
            throw new System.Exception($"response :{responseContent}", ex);
        }
        throw;
    }
}

GetAsync

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static readonly HttpClient Client = new HttpClient();
public async Task<string> GetAsync(string url, object data)
{
    try
    {
        string requestUrl = $"{url}?{GetQueryString(data)}";
        logger.Info($"GetAsync Start, requestUrl:{requestUrl}");
        var response = await Client.GetAsync(requestUrl).ConfigureAwait(false);
        string result = await response.Content.ReadAsStringAsync();
        logger.Info($"GetAsync End, requestUrl:{requestUrl}, HttpStatusCode:{response.StatusCode}, result:{result}");
        return result;
    }
    catch (WebException ex)
    {
        if (ex.Response != null)
        {
            string responseContent = new StreamReader(ex.Response.GetResponseStream()).ReadToEnd();
            throw new Exception($"Response :{responseContent}", ex);
        }
        throw;
    }
}

private static string GetQueryString(object obj)
{
    var properties = from p in obj.GetType().GetProperties()
                        where p.GetValue(obj, null) != null
                        select p.Name + "=" + HttpUtility.UrlEncode(p.GetValue(obj, null).ToString());

    return String.Join("&", properties.ToArray());
}

This sheet is to record abbreviation in my daily work as a software engineer.

1. Copy existing jenkins folder, exclude workspace
2. Modify jenkins port in Jenkins.xml, default 8080
3. Modify AD Domain and rename an account to yours in config.xml

4. Create / Start Jenkins service in cmd with administrator mode:

   1 2	sc create <jenkins-service-name> <path/to/jenkins.exe> sc start <jenkins-service-name>

5. View migrated jenkins in your browser with port specify above, default http://localhost:8080

If you want to understand how Redux work, createStore(reducer) is the core function you should know and try to implement yourself. Here is a basic example of Redux, don’t worry I will break it down later :

1. Use React.PureComponent, it implement shouldComponentUpdate() by shallow compare prop and state, it is powerful with Immutable.js.
2. Use Chrome extension and checked highlight updates in dev tool to find any unnecessary updates.
3. Use React-virtualized for render huge list in small chunk at a time.

4. Use Production build, for example with webpack you need following config:

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   new webpack.DefinePlugin({ 'process.env.NODE_ENV': JSON.stringify('production') }), new webpack.optimize.UglifyJsPlugin()

Before Start

Make sure the server has internet access or you will have to download and upload packages manually. If the server doesn’t, I recommend CCProxy to grant temporary internet access.

Install JDK

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wget -c --header "Cookie: oraclelicense=accept-securebackup-cookie" http://download.oracle.com/otn-pub/java/jdk/8u161-b12/2f38c3b165be4555a1fa6e98c45e0808/jdk-8u161-linux-x64.rpm
rpm -ivh jdk-8u161-linux-x64.rpm

Elasticsearch

1. Download and install

   1 2	wget https://artifacts.elastic.co/downloads/elasticsearch/elasticsearch-6.2.3.rpm rpm -ivh elasticsearch-6.2.3.rpm

2. Start service

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   # Auto start elasticsearch when computer start systemctl daemon-reload systemctl enable elasticsearch.service # start service systemctl start elasticsearch systemctl status elasticsearch

3. Verify Elastic search is running

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   curl http://localhost:9200 # If not working, you could try reboot reboot -r

   You could check log files under /var/log/elasticsearch/

4. Reference : https://www.elastic.co/guide/en/elasticsearch/reference/current/rpm.html

Kibana

1. Download and install

   1 2	wget https://artifacts.elastic.co/downloads/kibana/kibana-6.2.3-x86_64.rpm rpm -ivh kibana-6.2.3-x86_64.rpm

2. Modify kibana config

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   vi /etc/kibana/kibana.yml # Kibana port server.port: 5601 # Bind to all ip address server.host: "0.0.0.0"

3. Start service

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   systemctl daemon-reload systemctl enable kibana.service systemctl start kibana systemctl status kibana

4. Verify installation

   1	curl localhost:5601

   You can check log file under /var/log/kibana/

5. Reference : https://www.elastic.co/guide/en/kibana/current/rpm.html

Logstash

1. Download and install

   1 2	wget https://artifacts.elastic.co/downloads/logstash/logstash-6.2.3.rpm rpm -ivh logstash-6.2.3.rpm

2. Modify logstash.yml to enable auto reload config

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   vi /etc/logstash/logstash.yml config.reload.automatic: true config.reload.interval: 3s

3. Add first logstash config

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   cd /etc/logstash/conf.d/ cat > default.conf input { beats { port => 5044 } } output { elasticsearch { hosts => ["http://localhost:9200"] } }

4. Start service

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   systemctl daemon-reload systemctl enable logstash.service systemctl start logstash systemctl status logstash

5. Verify installation

   1	telnet 127.0.0.1 5044

   You could check log file under /var/log/logstash/

6. Reference : https://www.elastic.co/guide/en/logstash/current/installing-logstash.html