1. Architecture and Communication Model:
- REST is an architectural style for building web services that relies on a stateless, client-server communication model. The client sends requests to the server with all necessary data and receives responses in standardized formats like JSON or XML.
- RPC, on the other hand, is a communication model where a client calls a function on another computer as if it were local to that machine. The remote procedure call returns data directly back to the calling process after execution.
2. Request-Response vs Procedure Call:
- In REST, communication between client and server is based on requesting resources (represented by URIs) with HTTP methods like GET,What is the difference between REST and RPC
POST, PUT or DELETE. The client receives a response in the form of data about that resource and its state changes if applicable (e.g., after creating/updating/deleting it).
- In RPC, the client sends a message to call a specific function on another machine. The server processes this request and returns control back to the caller after execution with an appropriate response or result based on its implementation of that function.
3. Stateless vs Stateful:
- REST is considered stateless, meaning none of the context or session information about previous requests made by a client are maintained on the server-side between requests.
- RPC can be both stateless and stateful, depending on how its implementation handles session management and data persistence across multiple calls. However, most implementations involve some level of state maintenance to support function call chaining or maintain user contexts (e.g., in a client-server application).
4. Scalability and Flexibility:
- REST is designed to be highly scalable as it allows multiple clients to access shared resources concurrently via unique URIs. It also enables caching at various levels for better performance and reduces network traffic through data representation standardization (JSON, XML).
- RPC can achieve similar scalability with techniques like load balancing or clustering but requires more coordination between client and server due to its reliance on procedure calls for communication.
5. Heterogeneity:
- REST is platform-agnostic, meaning clients and servers can communicate regardless of their underlying technology or programming language as long as they adhere to standardized communication protocols (HTTP methods & formats like JSON, XML).
- RPC is typically restricted to homogeneous systems since it relies on specific interfaces and APIs that are often tied to particular programming languages or frameworks. However, technologies like gRPC aim at addressing thisWhat is the difference between REST and RPC
limitation by providing cross-platform capabilities using Protocol Buffers as the data serialization format.
Overall, REST is more flexible and allows for a greater separation of concerns between client and server compared to RPC since it relies on standardized HTTP methods for communication. However, depending on the specific use case or system requirements, one might choose either architecture based on factors such as performance needs, data representation preferences (JSON vs XML), and desired levels of flexibility.
nslookup not working on linux
If `nslookup` is not working on Linux, here are some steps you can take to troubleshoot the issue:
1. Check if nslookup is installed: You can check if `nslookup` is already installed on your Linux system by running the following command in a terminal or console window:
`bash
nslookup --version
`
If `nslookup` is not installed, you can install it using your package manager. For example, on Ubuntu or Debian-based systems, run:
`
sudo apt update && sudo apt install bind9-tools -y
`
2. Check network connection: Ensure that your system has a stable internet connection before trying to use `nslookup`. You can check the connectivity of your Linux machine by pinging an external server using its IP address or hostname:
`bash
ping google.com
`
3. Permission issues: Make sure that you have sufficient permissions to run `nslookup`. If it's not running with root privileges, try prefixing the command with "`sudo`":
`bash
sudo nslookup example.com
`
4. Check DNS server: You can check which nameserver your system is using to perform name resolution by running the following command in a terminal or console window (replace `your-interface` with the appropriate network interface):
`bash
cat /etc/resolv.conf | grep "nameserver" -A 3 | awk '{print $2}'
`
If the DNS server is not reachable or incorrect, you can modify your `/etc/resolv.conf` file to use a different one.
5. Firewall rules: Ensure that there are no firewall rules blocking the outgoing DNS requests on your Linux system (port 53 UDP/TCP). You can check for any active iptables or firewalld rules using the following commands:
`bash
sudo iptables --list-rules ---protocol all --match udp --dport 53 -j ACCEPT && \
sudo iptables --list-rules ---protocol tcp --dport 53 -j ACCEPT || echo "No rules found"
`
If firewall rules are present, you need to add the necessary exceptions. For example: on Ubuntu with iptables (`sudo ufw allow from any dns in up`, or create a custom rule).
6. BIND9 configuration: If your system uses the `bind9` DNS server and there are misconfigurations, you may encounter issues with nslookup. In this case, try checking your configuration files for any errors:
`bash
sudo systemctl status bind9 && \
grep -r "error" /etc/bind | less --tabsize=80 || echo "No errors found."
`
Confirm that your BIND9 is listening on the appropriate interfaces and ports as well: `sudo netstat -anp | grep bind`.
7. Reinstalling BIND9 DNS server software or using an alternative like `dnsmasq` can also be a potential solution, as this may resolve any underlying configuration issues.
8. If none of the above steps help in resolving the issue with `nslookup` on Linux, it might be worth considering reaching out to your network administrator or internet service provider for further assistance.
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