When your react.js app loads, the routes are handled on the frontend by the react-router. Say for example you are at http://a.com. Then on the page you navigate to http://a.com/b. This route change is handled in the browser itself. Now when you refresh or open the url http://a.com/b in the a new tab, the request goes to your nginx where the particular route does not exist and hence you get 404.

To avoid this, you need to load the root file(usually index.html) for all non matching routes so that nginx sends the file and the route is then handled by your react app on the browser. To do this you have to make the below change in your nginx.conf or sites-enabled appropiately

location / {
 try_files $uri /index.html;
}

This tells nginx to look for the specified $uri, if it cannot find one then it send index.html back to the browser. (See https://serverfault.com/questions/329592/how-does-try-files-work for more details)

The answers given here are correct. But, I was struggling with this when trying to deploy my React Application in a docker container. The problem was on, how to change the nginx configs inside a docker container.

Step 1: Prepare your Dockerfile

# Stage 1
FROM node:8 as react-build
WORKDIR /app
COPY . ./
RUN yarn
RUN yarn build

# Stage 2 - the production environment
FROM nginx:alpine
COPY nginx.conf /etc/nginx/conf.d/default.conf
COPY --from=react-build /app/build /usr/share/nginx/html
EXPOSE 80
CMD ["nginx", "-g", "daemon off;"]

See line with command: COPY nginx.conf /etc/nginx/conf.d/default.conf. Here, we are telling Docker to copy the nginx.conf file from the docker host, to the docker container.

Step 2: Have a nginx.conf file in your application root folder

server {
    listen       80;
    server_name  localhost;

    location / {
        root   /usr/share/nginx/html;
        index  index.html index.htm;
        try_files $uri /index.html;                 
    }

    error_page   500 502 503 504  /50x.html;
    location = /50x.html {
        root   /usr/share/nginx/html;
    }
}

Step 3: Now build the docker image and run it

$ docker build . -t react-docker

This should build your docker image successfully. To check that, run

$ docker images

Now run

$ docker run -p 8000:80 react-docker 

and navigate to http://localhost:8000

This was inspired by this blog.

For me the solution was:

location / {
            root /var/www/myapp/build;
            index index.html;
            try_files $uri /index.html$is_args$args =404;
    }