I think you may be confused, Flask is not a **web server**, it is a framework and needs some sort of web server, such as Gunicorn, Nginx or Apache, to accept HTTP requests which it will then operate on.  The reason why people run Nginx and Gunicorn together is that in addition to being a web server, Nginx can also proxy connections to Gunicorn which brings certain performance benefits, here is a pretty good answer that elaborates on those benefits:
https://serverfault.com/questions/220046/why-is-setting-nginx-as-a-reverse-proxy-a-good-idea

**EDIT:**
Added link containing information about performance benefits of running Nginx as a proxy.

**I&#39;m using Android Studio I/O(Preview) 0.3.2**

I&#39;m using [this example][1] to define background gradient in my app. I get Element must be declared error. ![enter image description here][2] 

I&#39;ve checked and I&#39;m not find any solutions. Can anyone help me how can I declare that tag in the xml


  [1]: https://stackoverflow.com/questions/14364617/how-can-i-add-gradient-effect-to-background-color-of-textview-in-a-listview
  [2]: http://i.stack.imgur.com/jLNTU.png

Element must be declared error for tag shape

I want to access the parent element of current element

Here is the structure of HTML

    svg
       g id=invisibleG
         g
           circle
         g
           circle
         g
           circle

Basically I want to add text inside the circles when I hover over them.

So I want something like this on hover of any particular circle

    svg
           g id=invisibleG
             g
               circle --&gt; radius is increased and text presented inside that
               text
             g
               circle
             g
               circle

On hover I can select current element through d3.select(this),How can I get root element(g in my case)?

How to select parent element of current element in d3.js

I see people are running setups like Nginx + Gunicorn + Flask.

Can someone explain what is the benefit of having Gunicorn in front of Flask? Why not just run Flask alone? Doesn&#39;t it consume more resources having Gunicorn + Flask running? Is Gunicorn able to reboot the Flask instance when it fails to respond?

What&#39;s also the purpose of having nginx on top of gunicorn? Isn&#39;t gunicorn enough? Again, more resources being spent?

What benefit is added by using Gunicorn + Nginx + Flask?

I see people are running setups like Nginx + Gunicorn + Flask.
Can someone explain what is the benefit of having Gunicorn in front of Flask? Why not just run Flask alone? Doesn't it consume more resources having Gunicorn + Flask running? Is Gunicorn able to reboot the Flask instance when it fails to respond?
What's also the purpose of having nginx on top of gunicorn? Isn't gunicorn enough? Again, more resources being spent?

Let&#39;s say I have this number `i = -6884376`.
How do I refer to it as to an unsigned variable?
Something like `(unsigned long)i` in C.

How to convert signed to unsigned integer in python

Which image processing techniques could be used to implement an application that detects the Christmas trees displayed in the following images?

&lt;img src=&quot;https://i.stack.imgur.com/nmzwj.png&quot; width=&quot;210&quot; height=&quot;150&quot;&gt; 
&lt;img src=&quot;https://i.stack.imgur.com/aVZhC.png&quot; width=&quot;210&quot; height=&quot;150&quot;&gt; 
&lt;img src=&quot;https://i.stack.imgur.com/2K9Ef.png&quot; width=&quot;210&quot; height=&quot;150&quot;&gt;

&lt;img src=&quot;https://i.stack.imgur.com/YowlH.png&quot; width=&quot;210&quot; height=&quot;150&quot;&gt;
&lt;img src=&quot;https://i.stack.imgur.com/2y4o5.png&quot; width=&quot;210&quot; height=&quot;150&quot;&gt;
&lt;img src=&quot;https://i.stack.imgur.com/FWhSP.png&quot; width=&quot;210&quot; height=&quot;150&quot;&gt;

I&#39;m searching for solutions that are going to work on all these images. Therefore, approaches that require training *haar cascade classifiers* or *template matching* are not very interesting.

I&#39;m looking for something that can be written in *any* programming language, *as long as* it uses only *Open Source* technologies. The solution must be tested with the images that are shared on this question. There are *6 input images* and the answer should display the results of processing each of them. Finally, for each *output image* there must be *red lines* draw to surround the detected tree.

How would you go about programmatically detecting the trees in these images?

  [1]: https://stackoverflow.com/a/20724615/176769
  [2]: https://stackoverflow.com/a/20624819/176769
  [3]: https://stackoverflow.com/a/9620295/176769

How to detect a Christmas Tree?

Python 3.2 introduced [Concurrent Futures][1], which appear to be some advanced combination of the older threading and [multiprocessing][2] modules.

What are the advantages and disadvantages of using this for CPU bound tasks over the older multiprocessing module?

[This article][3] suggests they&#39;re much easier to work with - is that the case?


  [1]: http://docs.python.org/3/library/concurrent.futures.html
  [2]: http://docs.python.org/2/library/multiprocessing.html
  [3]: http://eli.thegreenplace.net/2013/01/16/python-paralellizing-cpu-bound-tasks-with-concurrent-futures/

Concurrent.futures vs Multiprocessing in Python 3

I have a python 2.6 script (yes I know I should upgrade to at least 2.7) that looks like this:

    ret_code = 0
    
    def some_func()
      global ret_code
      ...

    if __name__ == &#39;__main__&#39;:
      global ret_code
      ...

Now I get a warning if I run the code:
*SyntaxWarning: name &#39;ret_code&#39; is assigned to before global declaration global ret_code*

Why do I get this warning?

I can solve the problem by doing so:


    def some_func()
          global ret_code
          ...

    if __name__ == &#39;__main__&#39;:
      global ret_code
      ret_code = 0 #assign 0 here instead of above
      ...

Still that doesn&#39;t answer my question. What is wrong with the original code?


global variable warning in python

I have a DataFrame with numerical values. What is the simplest way of appending a row (with a given index value) that represents the sum of each column?

Appending column totals to a Pandas DataFrame

I have one dedicated server in that server I deployed 5 nodejs application.

    domain name: www.nnd.com
    dedicated server ip: xxx.xx.x.60
I had domain which is pointed to my dedicated server ip.

sub domains are :

    app1.nnd.com pointed to xxx.xx.x.60
    app2.nnd.com pointed to xxx.xx.x.60
    app3.nnd.com pointed to xxx.xx.x.60
    app4.nnd.com pointed to xxx.xx.x.60
    app5.nnd.com pointed to xxx.xx.x.60


now in nginx configuration file based on the subdomain I need to route proxy.
Example:

    {
        listen:80;
        server_name:xxx.xx.x.60
        location / {
            #here based on subdomain of the request I need to create proxy_pass for my node application 
        }
    }

Is there any condition and how can I get the original domain name from proxy header?

route different proxy based on subdomain request in nginx

We use following nginx site configure file in our production env.

    log_format main &#39;$http_x_forwarded_for - $remote_user [$time_local] &quot;$request&quot; &#39;
                    &#39;$status $body_bytes_sent &quot;$http_referer&quot; &#39;
                    &#39;&quot;$http_user_agent&quot; $request_time&#39;;



    server {
            root /srv/www/web;
            server_name *.test.com;
            access_log /var/log/nginx/xxx.test.com.access.log main;

Both &quot;http://a.test.com/ping&quot; and &quot;http://b.test.com/ping&quot; http request will be record in file xxx.test.com.access.log.

But there is a problem, nginx don&#39;t store &quot;domain name&quot; in xxx.test.com.access.log.

&quot;http://a.test.com/ping&quot; and &quot;http://b.test.com/ping&quot; share the same request &quot;Get /ping&quot;.

How can I record &quot;a.test.com&quot; or &quot;b.test.com&quot; in nginx log?

Full record url in nginx log

I was looking at using HAProxy and Nginx for load balancing, and I had some questions:

- Should I use JUST HAProxy over Nginx for the proxy server?
- Is there any reason to have HAProxy and Nginx installed on the same proxy server?

Thanks

HAProxy vs. Nginx

I am trying to modify the Nginx config file to remove a &quot;rewrite&quot;.

Currently, I have this config file:

    worker_processes  1;

    events {
        worker_connections  1024;
    }

    http {
        include       mime.types;
        default_type  application/octet-stream;
        sendfile        on;
        keepalive_timeout  65;
    	server {
    		listen      80;
    		server_name amc.local;
    		return 301 https://$host:8443/index.html;
    	}
    }

Now I want to reload this config file, I tried

    nginx -s reload
    nginx -c &lt;conf file&gt;
    nginx -s stop/start


In the log file, there is the line

    2014/01/22 11:25:25 [notice] 1310#0: signal process started

but the modifications are not loaded.


Reload Nginx configuration

Trying to deploy my first portal .

 I am getting 502 gateway timeout error in browser when i was sending the request through browser  

when i checked the logs , i got this error

     2014/02/03 09:00:32 [error] 16607#0: *1 connect() failed (111: Connection refused) while connecting to upstream, client: 14.159.131.19, server: foo.com, request: &quot;GET HTTP/1.1&quot;, upstream: &quot;fastcgi://127.0.0.1:9000&quot;, host: &quot;22.11.180.154&quot;


is there any problem related to permissions

nginx: connect() failed (111: Connection refused) while connecting to upstream

I want my model&#39;s primary key to be an autoincrementing integer. Here is how my model looks like

    class Region(db.Model):
        __tablename__ = &#39;regions&#39;
        id = db.Column(db.Integer, primary_key=True, autoincrement=True)
        name = db.Column(db.String(100))
        parent_id = db.Column(db.Integer, db.ForeignKey(&#39;regions.id&#39;))
        parent = db.relationship(&#39;Region&#39;, remote_side=id, primaryjoin=(&#39;Region.parent_id==Region.id&#39;), backref=&#39;sub-regions&#39;)
        created_at = db.Column(db.DateTime, default=db.func.now())
        deleted_at = db.Column(db.DateTime)

The above code creates my table but does not make `id` autoincrementing. So if in my insert query I miss the `id` field it gives me this error 

&gt; ERROR:  null value in column &quot;id&quot; violates not-null constraint

So I changed the `id` declaration to look like this

    id = db.Column(db.Integer, db.Sequence(&#39;seq_reg_id&#39;, start=1, increment=1),
                   primary_key=True)

Still the same error. What is wrong with the code above?

unable to create autoincrementing primary key with flask-sqlalchemy

I have a Flask web hosting with no access to `cron` command.

How can I execute some Python function every hour?

How to schedule a function to run every hour on Flask?

Using a python flask server, I want to be able to throw an http error response with the abort command and use a custom response string and a custom message in the body

    @app.errorhandler(400)
    def custom400(error):
        response = jsonify({&#39;message&#39;: error.message})
        response.status_code = 404
        response.status = &#39;error.Bad Request&#39;
        return response

    abort(400,&#39;{&quot;message&quot;:&quot;custom error message to appear in body&quot;}&#39;)

But the error.message variable comes up as an empty string.  I can&#39;t seem to find documentation on how to get access to the second variable of the abort function with a custom error handler

how to get access to error message from abort command when using custom error handler

I have a list of objects that I need to jsonify.  I&#39;ve looked at the flask jsonify docs, but I&#39;m just not getting it.

My class has several inst-vars, each of which is a string: `gene_id`, `gene_symbol`, `p_value`.  What do I need to do to make this serializable as JSON?

My naive code:

    jsonify(eqtls = my_list_of_eqtls)

Results in:

    TypeError: &lt;__main__.EqtlByGene object at 0x1073ff790&gt; is not JSON serializable

Presumably I have to tell jsonify how to serialize an `EqtlByGene`, but I can&#39;t find an example that shows how to serialize an instance of a class.

I&#39;ve been trying to follow some of the suggestions show below to create my own JSONEncoder subclass.  My code is now:

    class EqtlByGene(Resource):
     
        def __init__(self, gene_id, gene_symbol, p_value):
            self.gene_id = gene_id
            self.gene_symbol = gene_symbol
            self.p_value = p_value
    
    class EqtlJSONEncoder(JSONEncoder):
        def default(self, obj):
            if isinstance(obj, EqtlByGene):
                return {
                       &#39;gene_id&#39;     : obj.gene_id,
                       &#39;gene_symbol&#39; : obj.gene_symbol,
                       &#39;p_value&#39;     : obj.p_value
                }
            return super(EqtlJSONEncoder, self).default(obj)
    
    class EqtlByGeneList(Resource):
        def get(self):
            eqtl1 = EqtlByGene(1, &#39;EGFR&#39;, 0.1)
            eqtl2 = EqtlByGene(2, &#39;PTEN&#39;, 0.2)
            eqtls = [eqtl1, eqtl2]
            return jsonify(eqtls_by_gene = eqtls)

    api.add_resource(EqtlByGeneList, &#39;/eqtl/eqtlsbygene&#39;)
    app.json_encoder(EqtlJSONEncoder)
    if __name__ == &#39;__main__&#39;:
        app.run(debug=True)

When I try to reach it via curl, I get:

    TypeError(repr(o) + &quot; is not JSON serializable&quot;)



Flask jsonify a list of objects

In Flask, when I have several routes for the same function,
how can I know which route is used at the moment?

For example:

    @app.route(&quot;/antitop/&quot;)
    @app.route(&quot;/top/&quot;)
    @requires_auth
    def show_top():
        ....

How can I know, that now route was called using `/top/` or `/antitop/`?

**UPDATE**

I know about `request.path` I don&#39;t want use it, because the request can be rather complex, and I want repeat the routing logic in the function. I think that the solution with `url_rule` it the best one.

Flask: get current route

I am working with configuring Django project with Nginx and Gunicorn.

While I am accessing my port `gunicorn mysite.wsgi:application --bind=127.0.0.1:8001` in Nginx server, I am getting the following error in my error log file;

&gt; 2014/05/30 11:59:42 [crit] 4075#0: *6 connect() to 127.0.0.1:8001 failed (13: Permission denied) while connecting to upstream, client: 127.0.0.1, server: localhost, request: &quot;GET / HTTP/1.1&quot;, upstream: `&quot;http://127.0.0.1:8001/&quot;`, host: &quot;localhost:8080&quot;

Below is the content of my `nginx.conf` file;

    server {
        listen 8080;
        server_name localhost;
        access_log  /var/log/nginx/example.log;
        error_log /var/log/nginx/example.error.log;

        location / {
            proxy_pass http://127.0.0.1:8001;
            proxy_set_header X-Forwarded-For $remote_addr;
            proxy_set_header Host $http_host;
        }
    }

In the HTML page I am getting `502 Bad Gateway`.

What mistake am I doing?

(13: Permission denied) while connecting to upstream:[nginx]

I have a django app and trying to set it up with gunicorn first and later with supervisor and nginx.

The app is running with the normal django command perfectly like `python manage.py runserver`

I installed the gunicorn using pip like `pip install gunicorn` and django version is `1.5.3`

when i run the below command inside the virtual env like below

`gunicorn  hello.wsgi:application -b xx.xxx.xxx.xx:8000` and faced the error


    Traceback (most recent call last):
      File &quot;/root/Envs/proj/bin/gunicorn&quot;, line 9, in &lt;module&gt;
        load_entry_point(&#39;gunicorn==19.0.0&#39;, &#39;console_scripts&#39;, &#39;gunicorn&#39;)()
      File &quot;/root/Envs/proj/local/lib/python2.7/site-packages/gunicorn/app/wsgiapp.py&quot;, line 74, in run
        WSGIApplication(&quot;%(prog)s [OPTIONS] [APP_MODULE]&quot;).run()
      File &quot;/root/Envs/proj/local/lib/python2.7/site-packages/gunicorn/app/base.py&quot;, line 166, in run
        super(Application, self).run()
      File &quot;/root/Envs/proj/local/lib/python2.7/site-packages/gunicorn/app/base.py&quot;, line 71, in run
        Arbiter(self).run()
      File &quot;/root/Envs/proj/local/lib/python2.7/site-packages/gunicorn/arbiter.py&quot;, line 169, in run
        self.manage_workers()
      File &quot;/root/Envs/proj/local/lib/python2.7/site-packages/gunicorn/arbiter.py&quot;, line 477, in manage_workers
        self.spawn_workers()
      File &quot;/root/Envs/proj/local/lib/python2.7/site-packages/gunicorn/arbiter.py&quot;, line 537, in spawn_workers
        time.sleep(0.1 * random.random())
      File &quot;/root/Envs/proj/local/lib/python2.7/site-packages/gunicorn/arbiter.py&quot;, line 209, in handle_chld
        self.reap_workers()
      File &quot;/root/Envs/proj/local/lib/python2.7/site-packages/gunicorn/arbiter.py&quot;, line 459, in reap_workers
        raise HaltServer(reason, self.WORKER_BOOT_ERROR)
    gunicorn.errors.HaltServer: &lt;HaltServer &#39;Worker failed to boot.&#39; 3&gt;

So why actually the above error is encountered and whats the fix ?

gunicorn.errors.HaltServer: &lt;HaltServer &#39;Worker failed to boot.&#39; 3&gt; django

I wrote a flask app using the application factory pattern.  That means it doesn&#39;t create an app instance automatically when you import it.  You have to call create_app for that.  Now how do I run it in gunicorn?

How do I run a flask app in gunicorn if I used the application factory pattern?

I want to know what exactly it means when a web server describes itself as a pre-fork web server. I have a few examples such as [unicorn][1] for ruby and [gunicorn][2] for python.

More specifically, these are the questions:

- What problem does this model solve?
- What happens when a pre-fork web server is initially started?
- How does it handle requests?

Also, a more specific question for unicorn/gunicorn:

Let&#39;s say that I have a webapp that I want to run with (g)unicorn. On initialization, the webapp will do some initialization stuff (e.g. fill in additional database entries). If I configure (g)unicorn with multiple workers, will the initialization stuff be run multiple times?

  [1]: http://unicorn.bogomips.org/
  [2]: http://gunicorn.org/

What exactly is a pre-fork web server model?

I&#39;m trying to add logging to a web application which uses Flask.

When hosted using the built-in server (i.e. `python3 server.py`), logging works. When hosted using Gunicorn, the log file is not created.

The simplest code which reproduces the problem is this one:

    #!/usr/bin/env python

    import logging
    from flask import Flask
    flaskApp = Flask(__name__)


    @flaskApp.route(&#39;/&#39;)
    def index():
        flaskApp.logger.info(&#39;Log message&#39;)
        print(&#39;Direct output&#39;)
        return &#39;Hello World\n&#39;


    if __name__ == &quot;__main__&quot;:
        logHandler = logging.FileHandler(&#39;/var/log/demo/app.log&#39;)
        logHandler.setLevel(logging.INFO)
        flaskApp.logger.addHandler(logHandler)
        flaskApp.logger.setLevel(logging.INFO)
        flaskApp.run()

The application is called using:

    gunicorn server:flaskApp -b :80 -w 4
        --access-gfile /var/log/demo/access.log
        --error-logfile /var/log/demo/error.log

When doing a request to the home page of the site, the following happens:

 1. I receive the expected HTTP 200 &quot;Hello World\n&quot; in response.

 1. There is a trace of the request in `/var/log/demo/access.log`.

 1. `/var/log/demo/error.log` stays the same (there are just the boot events).

 1. There is the &quot;Direct output&quot; line in the terminal.

 1. There is no &#39;/var/log/demo/app.log&#39;. If I create the file prior to launching the application, the file is not modified.

Note that:

 - The directory `/var/log/demo` can be accessed (read, write, execute) by everyone, so this is not the permissions issue.

 - If I add `StreamHandler` as a second handler, there is still no trace of the &quot;Log message&quot; message neither in the terminal, nor in Gunicorn log files.

 - Gunicorn is installed using `pip3 install gunicorn`, so there shouldn&#39;t be any mismatch with Python versions.

What&#39;s happening?

Content Type	Original Author	Original Content on Stackoverflow
Question	KJW	View Question on Stackoverflow
Solution 1 - Python	Jon	View Answer on Stackoverflow

What benefit is added by using Gunicorn + Nginx + Flask?

Python Problem Overview

Python Solutions

Solution 1 - Python

How to select parent element of current element in d3.js

Element must be declared error for tag shape

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