Tethering

In iOS when you enable the Personal Hotspot, it creates a separate bridge100 interface. So your tethered traffic goes out over this interface instead of the one your device traffic uses. So it counts against your tethered traffic instead of device traffic.

There is a way to make the tethered traffic use the same outbound interface that device traffic uses. This is a walk-through of how to do that.

First, install a-shell on iOS. Run it and enter pip install pvpn (see pvpn).

Then enter pvpn -wg 9000. You should see something like this: Copy the PublicKey it prints.

Next install the macOS WireGuard client

Choose Add Empty Tunnel…, name it pvpn and configure similar to this, where [Peer] PublicKey is the key the server printed above:

Activate the WireGuard tunnel while you are tethered to the iOS Personal Hotspot, and macOS traffic should now be routed over the VPN running on the iOS device.

You can confirm both the iOS device and the macOS client have the same public IP by visiting http://ifconfig.co/ in...

Why rectalogic?

Years ago I found a company called analogic.

I thought it was brave that they put anal front and center in their name. Even their logo kind of looks like a techno-stylized puckered hole

So I figured if an international corporation can choose this name, I can do something similar.

Other words that make me laugh:

analyze, therapist, banal, the ASS file format

I turn 12 in February.

Haystack Arq 5 APFS Snapshot Backup

Arq 5 backup on macOS does not automatically create and back up from an APFS snapshot.

By configuring Arq preferences with before and after backup scripts, you can take an APFS snapshot, mount it and perform the backup from the snapshot, then unmount when finished. This way the backup is point-in-time consistent.

snapshot-before.sh

#!/usr/bin/env bash

diskutil unmount /tmp/snapshot
set -o errexit

tmutil localsnapshot
SNAPSHOT=$(tmutil listlocalsnapshots / | tail -n 1)
mkdir -p /tmp/snapshot
mount -t apfs -r -o -s=$SNAPSHOT / /tmp/snapshot

snapshot-after.sh

#!/usr/bin/env bash

set -o errexit

diskutil unmount /tmp/snapshot

Run snapshot-before.sh manually and then in Arq select your home directory inside the snapshot as the directory to back up (/tmp/snapshot/Users/XXX).

PostgreSQL rowcount with SQLAlchemy/psycopg2 Streaming Cursor

SQLAlchemy ResultProxy.rowcount does work with SELECT statements when using psycopg2 with PostgreSQL, despite the warnings - as long as you aren’t streaming the results. This is because psycopg2 uses libpq PQexec along with PQcmdTuples to retreive the result count (PQexec always collects the command’s entire result, buffering it in a single PGresult).

Using SQLAlchemy stream_results causes psycopg2 to use a named server-side cursor via PostgreSQL DECLARE. This will stream result records on demand, but ResultProxy.rowcount will not reflect the total result count.

To workaround this you can configure the psycopg2 server-side cursor to be scrollable (this allows moving backwards in the resultset). Then after the streaming query, execute MOVE FORWARD ALL to move to the end of the results without fetching any. PQcmdTuples will then set the pscyopg2 rowcount and you can then scroll absolute back to the beginning of the results and process them streaming.

>>> import sqlalchemy as sa >>> >>> table =...
      
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      AWS VPN with Public Subnet

      
        This describes how to configure an ipsec VPN in an AWS VPC with a customer who does not allow RFC-1918 (private) IP addresses in the VPC subnet.
 The basic idea is to expose a single host in the VPN using a /32 subnet of the VPN public IP. We can restrict each client peer to a specific port on that host and use port forwarding to connect them to internal hosts on private subnets in the VPC. So we can support multiple clients, and each client sees only a single host (with a public IP) and can access a single client specific port on that host.
 The following applies to Ubuntu 14.04 and Strongswan 5.1.2. For purposes of discussion we have two clients. All public IPs are invalid examples. First, clientA with peer public IP 165.{A}.22.101 and an internal host with public IP 165.{A}.22.102. We will restrict clientA to port 2575. Second, clientB with peer public IP 180.{B}.89.101 and an internal host with public IP 180.{B}.89.102. We will restrict clientB to port 2576.
 We create an EC2 instance in a VPC with CIDR 10.0.0.0/16 and place it in a public subnet with CIDR 

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      IPsec Private Subnet

      
        Sometimes you want to secure local traffic in a private subnet for compliance reasons, e.g. HIPAA requires data in-transit to be encrypted. This can be done at the application level if the application supports SSL, but it can also be done independent of the application using IPsec transport layer encryption.
 In this example we have an AWS VPC with three Ubuntu 14.04 database instances in a private subnet running a mongodb replicaset with three members. We want to encrypt all mongodb traffic between replicaset members and between other client instances in the VPC and the mongodb instances - and we won’t use mongodb SSL support.
 The mad-hacking site has a good discussion of IPsec, racoon and setkey.
 First install ipsec-tools and racoon on each instance: sudo apt-get install ipsec-tools racoon.
 Create a pre-shared key file for use with ISAKMP. We are using the wildcard * to match all hosts, so all instances are using the same key. Generate this file once and install the same file on all instances:
 Generate the file with a random key:
 user@host$ echo "* " $(openssl rand -base64 48

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