Category: Technology

Migrating Redis Data

So, I know that Redis should be a data cache that can be repopulated … but we use it to calculate deltas (what was the value last time) … so repopulating the information makes the first half hour or so of calculations rather slow as the application tries redis, gets nothing, and fails back to a database query. Then we get a backlog of data to churn through, and it would just be better if the Redis cache hadn’t gone away in the first place. And if you own both servers and the files are in the same format, you could just copy the cache db from the old server to the new one. But … when you cannot just copy the file and you would really prefer the data not disappear and need to be repopulated … there’s a script for that! This python script reads all of the data from the “old” server and populates it into the “new” server. 

import redis

def migrate_data(redis_source_host, redis_source_port, redis_source_db, redis_source_password,
                 redis_dest_host, redis_dest_port, redis_dest_db, redis_dest_password):
    # Connect to the source Redis server
    source_client = redis.StrictRedis(host=redis_source_host, port=redis_source_port, db=redis_source_db, password=redis_source_password)

    # Connect to the destination Redis server
    dest_client = redis.StrictRedis(host=redis_dest_host, port=redis_dest_port, db=redis_dest_db, password=redis_dest_password)

    # Fetch all keys from the source Redis
    keys = source_client.keys('*')

    for key in keys:
        # Get the type of the key
        key_type = source_client.type(key).decode('utf-8')

        if key_type == 'string':
            value = source_client.get(key)
            print("Setting string value in dest")
            dest_client.set(key, value)
        elif key_type == 'list':
            values = source_client.lrange(key, 0, -1)
            print("Setting list value in dest")
            dest_client.delete(key)  # Ensure the list is empty before pushing
            for value in values:
                dest_client.rpush(key, value)
        elif key_type == 'set':
            values = source_client.smembers(key)
            print("Setting set value in dest")
            dest_client.delete(key)  # Ensure the set is empty before pushing
            for value in values:
                dest_client.sadd(key, value)
        elif key_type == 'zset':
            values = source_client.zrange(key, 0, -1, withscores=True)
            print("Setting zset value in dest")
            dest_client.delete(key)  # Ensure the zset is empty before pushing
            for value, score in values:
                dest_client.zadd(key, {value: score})
        elif key_type == 'hash':
            values = source_client.hgetall(key)
            print("Setting hash value in dest")
            dest_client.delete(key)  # Ensure the hash is empty before pushing
            dest_client.hmset(key, values)

    print("Data migration completed.")

if __name__ == "__main__":
    # Source Redis server details
    redis_source_host = 'oldredis.example.com'
    redis_source_port = 6379
    redis_source_db = 0
    redis_source_password = 'SourceRedisPassword'

    # Destination Redis server details
    redis_dest_host = 'newredis.example.com'
    redis_dest_port = 6379
    redis_dest_db = 0
    redis_dest_password = 'DestRedisPassword'

    # Migrate data
    migrate_data(redis_source_host, redis_source_port, redis_source_db, redis_source_password,
                 redis_dest_host, redis_dest_port, redis_dest_db, redis_dest_password)

SNMP Simulator

Background

As communication between development and production platforms is limited for security and data integrity reasons, this creates a challenge when testing changes in development: we cannot access “real world” data with which to perform tests. Having a limited set of data in development means testing may not illuminate issues that occur at high volume or on a large scale.

Solution

While limiting communication between the prod and dev systems is reasonable, it would be beneficial to be able to replay production-like data within our development systems for testing purposes. While it is not cost effective to buy large network devices with thousands of interfaces for testing, the Python module snmpsim provides “canned responses” that simulate real devise on the production network. For simplicity, I have a bash script that launches the SNMP responder.

server03:snmpsim # cat ../_playback.sh

#!/bin/bash

snmpsimd.py –data-dir=/opt/snmp/snmpsim/data –cache-dir=/opt/snmp/snmpsim/cache –agent-udpv4-endpoint=0.0.0.0:161 –process-user=ljrsnmp –process-group=ljrsnmp

This responder will replay data stored in the directory /opt/snmp/snmpsim/data – any file ending in snmprec will be included in the response, and the filename prior to .snmprec is the community string to access the response data. E.G. public.snmprec is the data for the public community string

The response files are in the format OID|TAG|VALUE where OID is the OID number of the SNMP object, TAG is an integer defined at https://pypi.org/project/snmpsim/0.2.3/

Valid tag values and their corresponding ASN.1/SNMP types are:

ASN.1/SNMP TypeTag Value
Integer322
Octet String4
Null5
Object Identifier6
IP Address64
Counter3265
Gauge3266
Time Ticks67
Opaque68
Counter6570

And the value is the data to be returned for the OID object. As an example:

1.3.6.1.2.1.1.3.0|67|2293092270

1.3.6.1.2.1.1.3.0 is the sysUpTime, the data type is TimeTicks, and the system up time is 2293092270 hundredths of a second. Or 6375 hours, 20 minutes, and 24 seconds.

Items within the response file need to be listed in ascending order.

Generating Response Data

There are two methods for creating the data provided to an SNMP GET request. A response file can be created manually, populated with OID objects that should be included in the response as well as sample data. Alternatively, a network trace can be gathered from the production network and parsed to create the response file.

Manually Generated Response File

While you can literally type data into a response file, but it is far easier to use a script to generate sample data. /opt/snmp/snmpsim/_genData.py is an example of creating a response file for about 1,000 interfaces

from datetime import datetime
import random

iRangeMax = 1000

dictTags = {'Integer': '2', 'OctetString': '4', 'NULL': '5', 'ObjectIdentifier': '6', 'IPAddress': '64', 'Counter32': '65', 'Gauge32': '66', 'TimeTicks': '67', 'Opaque': '68','Counter64': '70'}  # Valid tags per https://pypi.org/project/snmpsim/0.2.3/

today = datetime.now()

iftable_snmp_objects = [
    ('1.3.6.1.2.1.2.2.1.1', 'Integer', lambda i: i),  # ifIndex
    ('1.3.6.1.2.1.2.2.1.2', 'OctetString', lambda i: f"SampleInterface{i}"),  # ifDescr
    ('1.3.6.1.2.1.2.2.1.3', 'Integer', lambda i: 6),  # ifType
    ('1.3.6.1.2.1.2.2.1.4', 'Integer', lambda i: 1500),  # ifMtu
    ('1.3.6.1.2.1.2.2.1.5', 'Gauge32', lambda i: 100000000),  # ifSpeed
    ('1.3.6.1.2.1.2.2.1.6', 'OctetString', lambda i: f"00:00:00:00:{format(i, '02x')[:2]}:{format(i, '02x')[-2:]}"),  # ifPhysAddress
    ('1.3.6.1.2.1.2.2.1.7', 'Integer', lambda i: 1),  # ifAdminStatus
    ('1.3.6.1.2.1.2.2.1.8', 'Integer', lambda i: 1),  # ifOperStatus
    ('1.3.6.1.2.1.2.2.1.9', 'TimeTicks', lambda i: int((datetime.now() - datetime(2024, random.randint(1, today.month), random.randint(1, today.day))).total_seconds()) * 100),  # ifLastChange
    ('1.3.6.1.2.1.2.2.1.10', 'Counter32', lambda i: random.randint(3, i*50000)),  # ifInOctets
    ('1.3.6.1.2.1.2.2.1.11', 'Counter32', lambda i: random.randint(3, i*50000)),  # ifInUcastPkts
    ('1.3.6.1.2.1.2.2.1.12', 'Counter32', lambda i: random.randint(0, 80)),  # ifInNUcastPkts
    ('1.3.6.1.2.1.2.2.1.13', 'Counter32', lambda i: random.randint(0, 80)),  # ifInDiscards
    ('1.3.6.1.2.1.2.2.1.14', 'Counter32', lambda i: random.randint(0, 80)),  # ifInErrors
    ('1.3.6.1.2.1.2.2.1.15', 'Counter32', lambda i: random.randint(3, i*50000)),  # ifInUnknownProtos
    ('1.3.6.1.2.1.2.2.1.16', 'Counter32', lambda i: random.randint(3, i*50000)),  # ifOutOctets
    ('1.3.6.1.2.1.2.2.1.17', 'Counter32', lambda i: random.randint(3, i*50000)),  # ifOutUcastPkts
    ('1.3.6.1.2.1.2.2.1.18', 'Counter32', lambda i: random.randint(3, i*50000)),  # ifOutNUcastPkts
    ('1.3.6.1.2.1.2.2.1.19', 'Counter32', lambda i: random.randint(0, 80)),  # ifOutDiscards
    ('1.3.6.1.2.1.2.2.1.20', 'Counter32', lambda i: random.randint(0, 80)),  # ifOutErrors
]

ifxtable_snmp_objects = [
    ('1.3.6.1.2.1.31.1.1.1.1', 'OctetString', lambda i: f"SampleInterface{i}"),  # ifName
    ('1.3.6.1.2.1.31.1.1.1.15', 'Gauge32', lambda i: "100"),  # ifHighSpeed
    ('1.3.6.1.2.1.31.1.1.1.6', 'Counter32', lambda i: random.randint(3, i*50000)),  # ifHCInOctets
    ('1.3.6.1.2.1.31.1.1.1.10', 'Counter32', lambda i: random.randint(3, i*60000)),  # ifHCOutOctets
]

# Print IFTable data
for oid_base, tag_type, value_func in iftable_snmp_objects:
    for i in range(1, iRangeMax+1):
        value = value_func(i)
        print(f"{oid_base}.{i}|{dictTags.get(tag_type)}|{value}")

# IP-MIB objects for managing IP addressing
# ipAdEntAddr: The IP address to which this entry's addressing information pertains
print(f"1.3.6.1.2.1.4.20.1.1|{dictTags.get('IPAddress')}|10.5.5.5")

# ipAdEntIfIndex: The index value which uniquely identifies the interface to which this entry is applicable
print(f"1.3.6.1.2.1.4.20.1.2|{dictTags.get('OctetString')}|1")

# ipAdEntNetMask: The subnet mask associated with the IP address of this entry
print(f"1.3.6.1.2.1.4.20.1.3|{dictTags.get('OctetString')}|255.255.255.0")

# hrSWRunIndex: An index uniquely identifying a row in the hrSWRun table
print(f"1.3.6.1.2.1.25.4.2.1.1.1|{dictTags.get('Integer')}|1")

# hrSWRunName: The name of the software running on this device
print(f"1.3.6.1.2.1.25.4.2.1.2.1|{dictTags.get('OctetString')}|LJRSNMPAgent")
# hrSWRunID: The product ID of the software running on this device
print(f"1.3.6.1.2.1.25.4.2.1.3.1|{dictTags.get('ObjectIdentifier')}|1.3.6.1.4.1.25709.55")

# hrSWRunPath: The path of the software running on this device
print(f"1.3.6.1.2.1.25.4.2.1.4.1|{dictTags.get('OctetString')}|/opt/snmp/snmpsim/_agent.sh")

# hrSWRunParameters: Operational parameters for the software running on this device
print(f"1.3.6.1.2.1.25.4.2.1.5.1|{dictTags.get('OctetString')}|-L")

# hrSWRunType: The type of software running (e.g., operating system, application)
print(f"1.3.6.1.2.1.25.4.2.1.6.1|{dictTags.get('Integer')}|4")

# hrSWRunStatus: The status of this software (running, runnable, notRunnable, invalid)
print(f"1.3.6.1.2.1.25.4.2.1.7.1|{dictTags.get('Integer')}|1")


for oid_base, tag_type, value_func in ifxtable_snmp_objects:
    for i in range(1, iRangeMax+1):
        value = value_func(i)
        print(f"{oid_base}.{i}|{dictTags.get(tag_type)}|{value}")

Network Capture

Even better, parse a network capture file.

Capture Data

On the server that gathers SNMP data from the host we want to simulate, use a network capture utility to gather the SNMP communication between the server and the desired device.

tcpdump -i <interface> -w <filename>.pcap

E.G. to record the communication with 10.5.171.114

tcpdump ‘host 10.5.171.114 and (tcp port 161 or tcp port 162 or udp port 161 or udp port 162)’ -w /tmp/ar.pcap

Note – there Is no benefit to capturing more than one cycle of SNMP responses. If data is captured immediately, that means the devices were in the middle of a cycle. End the capture and start a new one shortly. There should be no packets captured for a bit, then packets during the SNMP polling cycle, and then another pause until the next cycle.

Parsing The Capture Data Into A Response File

The following script parses the capture file into an snmprec response file – note, I needed to use 2.6.0rc1 of scapy to parse SNMP data. The 2.5.0 release version failed to parse most of the packets which I believe is related to https://github.com/secdev/scapy/issues/3900

from scapy.all import rdpcap, SNMP
from scapy.layers.inet import UDP
from scapy.packet import Raw
from scapy.layers.snmp import SNMP, SNMPvarbind, SNMPresponse, SNMPbulk
from scapy.all import conf, load_layer
from scapy.utils import hexdump

from scapy.all import UDP, load_contrib
from scapy.packet import bind_layers

import os
from datetime import datetime
import argparse

# Ensure Scapy's SNMP contributions are loaded
load_contrib("snmp")

def sort_by_oid(listSNMPResponses):
    """
    Sorts a list of "OID|TAG|Value" strings by the OID numerically and hierarchically.

    :param listSNMPResponses: A list of "OID|TAG|Value" strings.
    :return: A list of "OID|TAG|Value" strings sorted by OID.
    """
    # Split each element into a tuple of (OID list, original string), converting OID to integers for proper comparison
    oid_tuples = [(list(map(int, element.split('|')[0].split('.'))), element) for element in listSNMPResponses]

    # Sort the list of tuples by the OID part (the list of integers)
    sorted_oid_tuples = sorted(oid_tuples, key=lambda x: x[0])

    # Extract the original strings from the sorted list of tuples
    sorted_listSNMPResponses = [element[1] for element in sorted_oid_tuples]

    return sorted_listSNMPResponses

parser = argparse.ArgumentParser(description='This script converts an SNMP packet capture into a snmpsim response file')
parser.add_argument('--filename', '-f', help='The capture file to process', required=True)

args = parser.parse_args()
strFullCaptureFilePath = args.filename
strCaptureFilePath, strCaptureFileName = os.path.split(strFullCaptureFilePath)


# Valid tags per https://pypi.org/project/snmpsim/0.2.3/
dictTags = {'ASN1_INTEGER': '2', 'ASN1_STRING': '4', 'ASN1_NULL': '5', 'ASN1_OID': '6', 'ASN1_IPADDRESS': '64', 'ASN1_COUNTER32': '65', 'ASN1_GAUGE32': '66', 'ASN1_TIME_TICKS': '67', 'Opaque': '68','ASN1_COUNTER64': '70'}

listSNMPResponses = []
listSNMPResponses.append("1.3.6.1.2.1.25.4.2.1.1.1|2|1")
listSNMPResponses.append("1.3.6.1.2.1.25.4.2.1.2.1|4|LJRSNMPAgent")
listSNMPResponses.append("1.3.6.1.2.1.25.4.2.1.3.1|6|1.3.6.1.4.1.25709.55")
listSNMPResponses.append("1.3.6.1.2.1.25.4.2.1.4.1|4|/opt/snmp/snmpsim/_agent.sh")
listSNMPResponses.append("1.3.6.1.2.1.25.4.2.1.5.1|4|-L")
listSNMPResponses.append("1.3.6.1.2.1.25.4.2.1.6.1|2|4")
listSNMPResponses.append("1.3.6.1.2.1.25.4.2.1.7.1|2|1")
i = 0

if True:
    packets = rdpcap(strFullCaptureFilePath)
    # Packets are zero indexed, so packet 1 in script is packet 2 in Wireshark GUI
    #for i in range(0,4):
    for packet in packets:
        print(f"Working on packet {i}")
        i = i + 1
        if SNMP in packet:
            snmp_layer = packet[SNMP]
            if isinstance(packet[SNMP].PDU,SNMPresponse):
                snmp_response = snmp_layer.getfield_and_val('PDU')[1]
                if hasattr(snmp_response, 'varbindlist') and snmp_response.varbindlist is not None:
                    for varbind in snmp_response.varbindlist:
                        strOID = varbind.oid.val if hasattr(varbind.oid, 'val') else str(varbind.oid)
                        strValue = varbind.value.val if hasattr(varbind.value, 'val') else str(varbind.value)
                        strType = type(varbind.value).__name__
                        if dictTags.get(strType):
                            iType = dictTags.get(strType)
                        else:
                            iType = strType

                        if isinstance(strValue, bytes):
                            print(f"Decoding {strValue}")
                            strValue = strValue.decode('utf-8',errors='ignore')

                        print(f"OID: {strOID}, Type: {strType}, Tag: {iType}, Value: {strValue}")
                        listSNMPResponses.append(f"{strOID}|{iType}|{strValue}")
            else:
                print(f"Not a response -- type is {type(packet[SNMP].PDU)}")
        elif Raw in packet:
            print(f"I have a raw packet at {i}")
        else:
            print(dir(packet))
            print(f"No SNMP or Raw in {i}: {packet}")

# Sort by OID numbers
listSortedSNMPResponses = sort_by_oid(listSNMPResponses)
f = open(f'/opt/snmp/snmpsim/data/{datetime.now().strftime("%Y%m%d")}-{strCaptureFileName.rsplit(".", 1)[0]}.deactivated', "w")
for strSNMPResponse in listSortedSNMPResponses:
    print(strSNMPResponse)
    f.write(strSNMPResponse)
    f.write("\n")
f.close()

This will create an snmpsim response file at /opt/snmp/snmpsim/data named as the capture file prefixed with the current year, month, and date. I.E. My ar.cap file results are /opt/snmp/snmpsim/data/20240705-ar.deactivated – you can then copy the file to whatever community string you want – cp 20240705-ar.deactivated CommunityString.snmprec

Linux Command: Column

Column is an interesting command – it will turn delimited text into, well, columns. Simply tell it you want a table (-t) and indicate what separator to use (-s). Optionally, you can add table column headers

[lisa@linux01 ~/]# cat /etc/group | column -t -s :
root              x  0      root,lisa
bin               x  1
daemon            x  2
...
passim            x  987

Alternately, you can use -J to get JSON-formatted output. Here you need the –table-columns as a comma delimited list of column names:

[lisa@linux01 ~/]# cat /etc/group | column -J -s : --table-columns "group,password,gid,members"
{
   "table": [
      {
         "group": "root",
         "password": "x",
         "gid": "0",
         "members": "root,lisa"
      },{
         "group": "bin",
         "password": "x",
         "gid": "1",
         "members": null
      },{
         "group": "daemon",
         "password": "x",
         "gid": "2",
         "members": null
      },{
         "group": "passim",
         "password": "x",
         "gid": "987",
         "members": null
      }
   ]
}

Which can then be parsed with jq

[lisa@linux01 ~/]# cat /etc/group | column -J -s : --table-columns "group,password,gid,members" | jq '[.table[] | {group: .group, members: .members}]'
[
  {
    "group": "root",
    "members": "root,lisa"
  },
  {
    "group": "bin",
    "members": null
  },
  {
    "group": "daemon",
    "members": null
  },
  {
    "group": "passim",
    "members": null
  }
]

JPA/Hibernate Naming Strategies

One of the challenges of inheriting support of systems and code is reverse engineering what exactly you’ve got. In this case, I have Java code that reads from a Postgresql table named calculation_config & populates the information into a Redis cache. Except I could not find any text containing the string calculation_config. Started to wonder if grep was getting thrown off by line splits (although splitting a line in the middle of a table name is asking for future confusion), so was searching for sub-strings.

Which got me to the code that performs the operation — but the table is absolutely named calculationConfig in the code. ?????

package com.example.applicationmodel;
import lombok.Data;

import jakarta.persistence.*;

@Entity // This tells Hibernate to make a table out of this class
@Data // Lombok: adds getters and setters
@Table(name = "calculationConfig", schema = "components")
public class CalculationInfo {
    @Id
    private int functionId;
    private String dataCollectionGroup;
    private String component;
    private String metricInputs;
    private String metricName;
    private String functionDef;
    private String resourceType;
    private String metricDatatype;
    private String deviceModel;
    private String collectionSystem;
    private int status;
}

And today, I’ve learned about “naming strategies”. A mechanism used by the Hibernate ORM (Object-Relational Mapping) framework to map entities within Java code to table and column names. Other than obfuscation, why are we applying middleware principals to code?? Ostensibly because database naming “best practices” and code naming “best practices” vary. As an aside, I was taught the best naming best practice was one someone was likely to figure out with minimal confusion or research. Explicitly indicating the naming strategy might fit that requirement — ohh, here’s some strange name mapping thing in my code. Let me see what that means.

By default, Hibernate uses ImplicitNamingStrategy and PhysicalNamingStrategy to map Java names to database names. The default PhysicalNamingStrategyStandardImpl converts camelCase to snake_case.

So, for future reference … when I find table_name or field_name in my database, I should be grepping for tableName and fieldName in the code. That is … not super obvious.

OpenZFS On RedHat 8 (From Package)

This process presumes you have generated a signing key (/root/signing/MOK.priv and /root/signing/MOK.der) that has been registered for signing modules.

################################################################################
## Install from Repo and Sign Modules
################################################################################
yum install https://dl.fedoraproject.org/pub/epel/epel-release-latest-8.noarch.rpm
yum install kernel-devel

# Install kmod version of ZS
yum install https://zfsonlinux.org/epel/zfs-release-2-3$(rpm --eval "%{dist}").noarch.rpm
dnf config-manager --disable zfs
dnf config-manager --enable zfs-kmod
yum install zfs

# And autoload
echo zfs >/etc/modules-load.d/zfs.conf

# Use rpm -ql to list out the kernel modules that this version of ZFS uses -- 2.1.x has quite a few of them, and they each need to be signed
# Sign zfs.ko and spl.ko in current kernel
/usr/src/kernels/$(uname -r)/scripts/sign-file sha256 /root/signing/MOK.priv /root/signing/MOK.der /lib/modules/$(uname -r)/weak-updates/zfs/zfs/zfs.ko
/usr/src/kernels/$(uname -r)/scripts/sign-file sha256 /root/signing/MOK.priv /root/signing/MOK.der /lib/modules/$(uname -r)/weak-updates/zfs/spl/spl.ko
# And sign the bunch of other ko files in the n-1 kernel rev (these are symlinked from the current kernel)
/usr/src/kernels/$(uname -r)/scripts/sign-file sha256 /root/signing/MOK.priv /root/signing/MOK.der /lib/modules/4.18.0-513.18.1.el8_9.x86_64/extra/zfs/avl/zavl.ko
/usr/src/kernels/$(uname -r)/scripts/sign-file sha256 /root/signing/MOK.priv /root/signing/MOK.der /lib/modules/4.18.0-513.18.1.el8_9.x86_64/extra/zfs/icp/icp.ko
/usr/src/kernels/$(uname -r)/scripts/sign-file sha256 /root/signing/MOK.priv /root/signing/MOK.der /lib/modules/4.18.0-513.18.1.el8_9.x86_64/extra/zfs/lua/zlua.ko
/usr/src/kernels/$(uname -r)/scripts/sign-file sha256 /root/signing/MOK.priv /root/signing/MOK.der /lib/modules/4.18.0-513.18.1.el8_9.x86_64/extra/zfs/nvpair/znvpair.ko
/usr/src/kernels/$(uname -r)/scripts/sign-file sha256 /root/signing/MOK.priv /root/signing/MOK.der /lib/modules/4.18.0-513.18.1.el8_9.x86_64/extra/zfs/unicode/zunicode.ko
/usr/src/kernels/$(uname -r)/scripts/sign-file sha256 /root/signing/MOK.priv /root/signing/MOK.der /lib/modules/4.18.0-513.18.1.el8_9.x86_64/extra/zfs/common/zcommon.ko
/usr/src/kernels/$(uname -r)/scripts/sign-file sha256 /root/signing/MOK.priv /root/signing/MOK.der /lib/modules/4.18.0-513.18.1.el8_9.x86_64/extra/zfs/zstd/zzstd.ko

# Verify they are signed now
modinfo -F signer /usr/lib/modules/$(uname -r)/weak-updates/zfs/zfs/zfs.ko
modinfo -F signer /usr/lib/modules/$(uname -r)/weak-updates/zfs/spl/spl.ko

modinfo -F signer /lib/modules/4.18.0-513.18.1.el8_9.x86_64/extra/zfs/avl/zavl.ko
modinfo -F signer /lib/modules/4.18.0-513.18.1.el8_9.x86_64/extra/zfs/icp/icp.ko
modinfo -F signer /lib/modules/4.18.0-513.18.1.el8_9.x86_64/extra/zfs/lua/zlua.ko
modinfo -F signer /lib/modules/4.18.0-513.18.1.el8_9.x86_64/extra/zfs/nvpair/znvpair.ko
modinfo -F signer /lib/modules/4.18.0-513.18.1.el8_9.x86_64/extra/zfs/unicode/zunicode.ko
modinfo -F signer /lib/modules/4.18.0-513.18.1.el8_9.x86_64/extra/zfs/zcommon/zcommon.ko
modinfo -F signer /lib/modules/4.18.0-513.18.1.el8_9.x86_64/extra/zfs/zstd/zzstd.ko

# Reboot
init 6

# And we've got ZFS, so create the pool
zpool create pgpool sdc
zfs create zpool/zdata
zfs set compression=lz4 zpool/zdata

zfs get compressratio zpool/zdata
zfs set mountpoint=/zpool/zdata zpool/zdata

What happens if you only sign zfs.ko? All sorts of errors that look like there’s some sort of other problem — zfs will not load. It will tell you the required key is not available

May 22 23:42:44 sandboxserver systemd-modules-load[492]: Failed to insert 'zfs': Required key not available

Using insmod to try to manually load it will tell you there are dozens of unknown symbols:

May 22 23:23:23 sandboxserver kernel: zfs: Unknown symbol ddi_strtoll (err 0)
May 22 23:23:23 sandboxserver kernel: zfs: Unknown symbol spl_vmem_alloc (err 0)
May 22 23:23:23 sandboxserver kernel: zfs: Unknown symbol taskq_empty_ent (err 0)
May 22 23:23:23 sandboxserver kernel: zfs: Unknown symbol zone_get_hostid (err 0)
May 22 23:23:23 sandboxserver kernel: zfs: Unknown symbol tsd_set (err 0)

But the real problem is that there are unsigned modules so … there are unknown symbols. But not because something is incompatible. Just because the module providing that symbol will not load.

OpenZFS on RedHat 8 – Build from Source

This process presumes you have generated a signing key (/root/signing/MOK.priv and /root/signing/MOK.der) that has been registered for signing modules.

# Install prerequisites
dnf install --skip-broken epel-release gcc make autoconf automake libtool rpm-build libtirpc-devel libblkid-devel libuuid-devel libudev-devel openssl-devel zlib-devel libaio-devel libattr-devel elfutils-libelf-devel kernel-devel-$(uname -r) python3 python3-devel python3-setuptools python3-cffi libffi-devel git ncompress libcurl-devel

dnf install --skip-broken --enablerepo=epel --enablerepo=powertools python3-packaging dkms

# Clone OpenZFS repo
git clone https://github.com/openzfs/zfs
cd zfs
# generally stay in the main branch, but if you want to use the latest then check out the staging branch
# git checkout zfs-2.2.5-staging
./autogen.sh
./configure
make 
make install

# Sign the kernel modules
/usr/src/kernels/$(uname -r)/scripts/sign-file sha256 /root/signing/MOK.priv /root/signing/MOK.der /lib/modules/$(uname -r)/extra/zfs.ko
/usr/src/kernels/$(uname -r)/scripts/sign-file sha256 /root/signing/MOK.priv /root/signing/MOK.der /lib/modules/$(uname -r)/extra/spl.ko

# And verify the modules are signed
modinfo -F signer /usr/lib/modules/$(uname -r)/extra/zfs.ko
modinfo -F signer /usr/lib/modules/$(uname -r)/extra/spl.ko

Signing Kernel Modules

The new servers being built at work use SecureBoot — something that you don’t even notice 99% of the time. But that 1% where you are doing something “strange” like trying to use OpenZFS … well, you’ve got to sign any kernel modules that you need to use. Just installing them doesn’t work — they won’t load.

To sign a kernel module, first you need to create a signing key and use mokutil to import it into the machine owner key store. 

cd /root
mkdir signing
cd signing
openssl req -new -x509 -newkey rsa:2048 -keyout MOK.priv -outform DER -out MOK.der -nodes -days 36500 -subj "/CN=Windstream/"

mokutil --import MOK.der

When you run mokutil, you will set a password. This password will be needed to complete importing the key to the machine.

Get access to the console — out of band management, vSphere manager, stand in front of the server. Reboot, and there will be a “press any key” screen for ten seconds that begins the import process. Press any key!

Select “Enroll MOK”

View the key and verify it is the right one, then use ‘Continue’ to import it

Enter the password used when you ran mokutil

Then reboot

To verify your key has been successfully enrolled:

mokutil --list-enrolled

Postgresql with File System Compression – VDO and ZFS

Our database storage is sizable. To reduce the financial impact of storing so much data, we opted to use a compressed file system. This allows us to maintain, for example, 8TB of data in under 2TB of space. Unfortunately, the ZFS file system we use to compress our data is no longer “built in” with newer version of RedHat.

There are alternatives. BTRFS is a long-standing option, however it’s got reliability issues (we piloted BTRFS on one of the read only replicas, and the compression ratio is nowhere near as good — the 2TB of ZFS data filled the 10TB BTRFS disk even using the better compression option. And I/O was so slow there was a continual replication backlog). RedHat introduced Virtual Disk Optimizer to replace ZFS. In theory, it’s better since it also deduplicates data (e.g. if every one of us saved the same PPT presentation to the disk, only one copy would actually be stored). That’s great for email and file shares where a lot of people are likely to store the same information. Not so useful on a database server where there’s little to de-duplicate. It does, however, compress data … so we decided to try it out.

The results, unfortunately, are not spectacular. VDO does not allow you to do much customization of the compression. It’s on or off. I’ve found some people tweaking it up in unsupported ways, but the impetus behind trying VDO was that it’s supported by RedHat. Making unsupported changes to it defeats that purpose. And the compression that we’re seeing is far less than we get in ZFS. Our existing servers run between 4.5x and 6x compression

In VDO, however, we don’t even get a 2x compression factor. 11TB of information is stored in 8TB of space! That’s 1.4x

So, while we found the performance of VDO to be satisfactory and it’s really easy to use in newer RedHat releases … we’d have to increase our 20TB LUNs to 80TB to continue storing the data we store today. That seems like A Really Bad Idea(tm).

Seems like I’m going to have to sort out using OpenZFS on the new servers.