COPY need path with / at the end in Dockerfile

client/Dockerfile

 FROM node:10-alpine
 
-RUN mkdir -p /app
-WORKDIR /app
+RUN mkdir -p /app/
+WORKDIR /app/
 
 COPY . .
 

server/Dockerfile

 FROM node:10-alpine
 
-RUN mkdir -p /usr/src/app
-WORKDIR /usr/src/app
+RUN mkdir -p /usr/src/app/
+WORKDIR /usr/src/app/
 
 RUN npm install
 
-COPY package*.json /usr/src/app
+COPY package*.json /usr/src/app/
 RUN npm install
 
-COPY . /usr/src/app
+COPY . /usr/src/app/
 
 CMD ["npm", "start"]
\ No newline at end of file