Ilmar Kerm

Written by: ilmarkerm

Category: Blog entry

Published: April 14, 2024

Here I’m exploring how to control the basic network level resource security accesses. In AWS there is a concept called Security Groups. In OCI Oracle Cloud the similar concept is called Network Security Groups, also there is a little bit less powerful concept called Security Lists. A good imprevement with Network Security Groups over Security Lists is that in rules you can refer to other NSGs, not only CIDR.

Below I create two NSG – one for databases and one for application servers, and allow unrestricted outgoing traffc from them both.

# security.tf

# Rules for appservers

resource "oci_core_network_security_group" "appserver" {
    compartment_id = oci_identity_compartment.compartment.id
    vcn_id = oci_core_vcn.main.id
    display_name = "Application servers"
}

resource "oci_core_network_security_group_security_rule" "appserver_egress" {
    network_security_group_id = oci_core_network_security_group.appserver.id
    direction = "EGRESS"
    protocol = "all"
    description = "Allow all Egress traffic"
    destination = "0.0.0.0/0"
    destination_type = "CIDR_BLOCK"
}

# Rules for databases

resource "oci_core_network_security_group" "db" {
    compartment_id = oci_identity_compartment.compartment.id
    vcn_id = oci_core_vcn.main.id
    display_name = "Databases"
}

resource "oci_core_network_security_group_security_rule" "db_egress" {
    network_security_group_id = oci_core_network_security_group.db.id
    direction = "EGRESS"
    protocol = "all"
    description = "Allow all Egress traffic"
    destination = "0.0.0.0/0"
    destination_type = "CIDR_BLOCK"
}

Some rule examples to allow traffic from appservers towards databases. Here referring to the appserver NSG as source – not a CIDR.

# This rule allows port 1521/tcp to be accessed from NSG "appserver" created earlier
resource "oci_core_network_security_group_security_rule" "db_appserver_oracle" {
    network_security_group_id = oci_core_network_security_group.db.id
    direction = "INGRESS"
    protocol = "6" # TCP
    description = "Allow ingress from application servers to 1521/tcp"
    source_type = "NETWORK_SECURITY_GROUP"
    source = oci_core_network_security_group.appserver.id
    tcp_options {
        destination_port_range {
            min = 1521
            max = 1521
        }
    }
}

# This rule allows port 5432/tcp to be accessed from NSG "appserver" created earlier
resource "oci_core_network_security_group_security_rule" "db_appserver_postgres" {
    network_security_group_id = oci_core_network_security_group.db.id
    direction = "INGRESS"
    protocol = "6" # TCP
    description = "Allow ingress from application servers to 5432/tcp"
    source_type = "NETWORK_SECURITY_GROUP"
    source = oci_core_network_security_group.appserver.id
    tcp_options {
        destination_port_range {
            min = 5432
            max = 5432
        }
    }
}

And one example rule for appserver group, here I just want to show that the source NSG can refer to itself – so the port is open only to resources placed in the same NSG.

# This rule allows port 80/tcp to be accessed from the NSG itself
# Example use - the application is running unencrypted HTTP and is expected to have a loadbalancer in front, that does the encryption. In this case loadbalancer could be put to the same NSG.
# Or if the different application servers need to have a backbone communication port between each other - like cluster interconnect
resource "oci_core_network_security_group_security_rule" "appserver_http" {
    network_security_group_id = oci_core_network_security_group.appserver.id
    direction = "INGRESS"
    protocol = "6" # TCP
    description = "Allow access port port 80/tcp only from current NSG (self)"
    source_type = "NETWORK_SECURITY_GROUP"
    source = oci_core_network_security_group.appserver.id
    tcp_options {
        destination_port_range {
            min = 80
            max = 80
        }
    }
}

Now, network security groups need to be attached to the resources they are intended to protect. NSG-s are attached to the virtual network adapers VNICs.

To attach NSG to my previously created compute instance, I have to go back and edit the compute instance declaration to attach a NSG to the primary VNIC of that instance.

# compute.tf

resource "oci_core_instance" "arm_instance" {
    compartment_id = oci_identity_compartment.compartment.id
    # oci iam availability-domain list
    availability_domain = "MpAX:EU-STOCKHOLM-1-AD-1"
    # oci compute shape list --compartment-id 
    shape = "VM.Standard.A1.Flex" # ARM based shape
    shape_config {
        # How many CPUs and memory
        ocpus = 2
        memory_in_gbs = 4
    }
    display_name = "test-arm-1"
    source_details {
        # The source operating system image
        # oci compute image list --all --output table --compartment-id 
        source_id = data.oci_core_images.oel.images[0].id
        source_type = "image"
    }
    create_vnic_details {
        # Network details
        subnet_id = oci_core_subnet.subnet.id
        assign_public_ip = true
        # attaching Network Security Groups - NSGs
        nsg_ids = [oci_core_network_security_group.appserver.id]
    }
    # CloudInit metadata - including my public SSH key
    metadata = {
        ssh_authorized_keys = "ssh-rsa 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 ilmars_public_key"
    }
}